SQL/JSON Path Expressions

Received: from malur.postgresql.org ([217.196.149.56]) by arkaria.postgresql.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.89) (envelope-from ) id 1iD8Ya-0001et-Pl for pgsql-hackers@arkaria.postgresql.org; Wed, 25 Sep 2019 14:46:17 +0000 Received: from localhost ([127.0.0.1] helo=malur.postgresql.org) by malur.postgresql.org with esmtp (Exim 4.89) (envelope-from ) id 1iD8YZ-0002K0-Iy for pgsql-hackers@arkaria.postgresql.org; Wed, 25 Sep 2019 14:46:15 +0000 Received: from magus.postgresql.org ([2a02:c0:301:0:ffff::29]) by malur.postgresql.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.89) (envelope-from ) id 1iD8YY-0002Jt-Te for pgsql-hackers@lists.postgresql.org; Wed, 25 Sep 2019 14:46:15 +0000 Received: from cyclops.postgrespro.ru ([93.174.131.138] helo=mail.postgrespro.ru) by magus.postgresql.org with esmtp (Exim 4.89) (envelope-from ) id 1iD8YT-0005Lx-S7 for pgsql-hackers@postgresql.org; Wed, 25 Sep 2019 14:46:14 +0000 Received: from localhost (localhost [127.0.0.1]) by mail.postgrespro.ru (Postfix) with ESMTP id 8DC9221C415A; Wed, 25 Sep 2019 17:46:08 +0300 (MSK) X-Virus-Scanned: Debian amavisd-new at postgrespro.ru X-Spam-Flag: NO X-Spam-Score: 0 X-Spam-Level: X-Spam-Status: No, score=x tagged_above=-99 required=4 WHITELISTED tests=[] autolearn=unavailable Received: from [192.168.27.64] (gw.postgrespro.ru [93.174.131.141]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client did not present a certificate) by mail.postgrespro.ru (Postfix) with ESMTPSA id 3742221C3F9F; Wed, 25 Sep 2019 17:46:08 +0300 (MSK) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=postgrespro.ru; s=mail; t=1569422768; bh=oQRznuyxWOFHDBHUMAlFwgJJ4KgA1sC5RYCH75Qeaa0=; h=Subject:To:Cc:References:From:Date:In-Reply-To; b=pHyULZvyt72zQYOCB5T9Srs9fPPSYPGy3MWD9fYMs6XsIvoO9UPzohTiyXasG4FeI IgGKbBqJMVf8XewD6hDyb13QWz0nLDdqLvWyhdLqliacmA9aHnp4WJAk2NNpILw/MG 0OwRfDbMKrYEHah4RGnEzCwBfQZG1wxiU9psnbyc= Subject: Re: JSONPATH documentation To: Peter Eisentraut , Tom Lane , Alexander Korotkov Cc: Jeff Janes , pgsql-hackers References:

<16968.1569189812@sss.pgh.pa.us> <96fb58c4-6281-b201-b900-03d0a84f77ac@2ndquadrant.com> From: Liudmila Mantrova Message-ID: Date: Wed, 25 Sep 2019 17:46:08 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <96fb58c4-6281-b201-b900-03d0a84f77ac@2ndquadrant.com> Content-Type: multipart/mixed; boundary="------------3479AF35BF75E785ECC268AB" Content-Language: en-US List-Id: List-Help: List-Subscribe: List-Post: List-Owner: List-Archive: Precedence: bulk This is a multi-part message in MIME format. --------------3479AF35BF75E785ECC268AB Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit On 9/25/19 12:08 AM, Peter Eisentraut wrote: > On 2019-09-23 00:03, Tom Lane wrote: >> While we're whining about this, I find it very off-putting that >> the jsonpath stuff was inserted in the JSON functions section >> ahead of the actual JSON functions. I think it should have >> gone after them, because it feels like a barely-related interjection >> as it stands. Maybe there's even a case that it should be >> its own , after the "functions-json" section. > I'd just switch the sect2's around. As more SQL/JSON functionality gets added, I believe a separate sect1 is likely to be more justified. However, for v12 I'd vote for moving sect2 down. The patch is attached, it also fixes the ambiguous sentence that has raised questions in this thread. -- Liudmila Mantrova Technical writer at Postgres Professional: http://www.postgrespro.com The Russian Postgres Company --------------3479AF35BF75E785ECC268AB Content-Type: text/x-patch; name="move-jsonpath.patch" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="move-jsonpath.patch" diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml index 432dbad868..6c4444b5d6 100644 --- a/doc/src/sgml/func.sgml +++ b/doc/src/sgml/func.sgml @@ -11646,14 +11646,14 @@ table2-mapping - SQL/JSON path expressions - (see ). + PostgreSQL-specific functions and operators for JSON + data types (see ). - PostgreSQL-specific functions and operators for JSON - data types (see ). + SQL/JSON path expressions + (see ). @@ -11665,1748 +11665,1748 @@ table2-mapping see . - - SQL/JSON Path Expressions + + JSON Functions and Operators - SQL/JSON - path expressions + JSON + functions and operators - SQL/JSON path expressions specify the items to be retrieved - from the JSON data, similar to XPath expressions used - for SQL access to XML. In PostgreSQL, - path expressions are implemented as the jsonpath - data type and can use any elements described in - . + shows the operators that + are available for use with JSON data types (see ). - JSON query functions and operators - pass the provided path expression to the path engine - for evaluation. If the expression matches the queried JSON data, - the corresponding SQL/JSON item is returned. - Path expressions are written in the SQL/JSON path language - and can also include arithmetic expressions and functions. - Query functions treat the provided expression as a - text string, so it must be enclosed in single quotes. - + + <type>json</type> and <type>jsonb</type> Operators + + + + Operator + Right Operand Type + Return type + Description + Example + Example Result + + + + + -> + int + json or jsonb + Get JSON array element (indexed from zero, negative + integers count from the end) + '[{"a":"foo"},{"b":"bar"},{"c":"baz"}]'::json->2 + {"c":"baz"} + + + -> + text + json or jsonb + Get JSON object field by key + '{"a": {"b":"foo"}}'::json->'a' + {"b":"foo"} + + + ->> + int + text + Get JSON array element as text + '[1,2,3]'::json->>2 + 3 + + + ->> + text + text + Get JSON object field as text + '{"a":1,"b":2}'::json->>'b' + 2 + + + #> + text[] + json or jsonb + Get JSON object at the specified path + '{"a": {"b":{"c": "foo"}}}'::json#>'{a,b}' + {"c": "foo"} + + + #>> + text[] + text + Get JSON object at the specified path as text + '{"a":[1,2,3],"b":[4,5,6]}'::json#>>'{a,2}' + 3 + + + +

+ + + There are parallel variants of these operators for both the + json and jsonb types. + The field/element/path extraction operators + return the same type as their left-hand input (either json + or jsonb), except for those specified as + returning text, which coerce the value to text. + The field/element/path extraction operators return NULL, rather than + failing, if the JSON input does not have the right structure to match + the request; for example if no such element exists. The + field/element/path extraction operators that accept integer JSON + array subscripts all support negative subscripting from the end of + arrays. + + - A path expression consists of a sequence of elements allowed - by the jsonpath data type. - The path expression is evaluated from left to right, but - you can use parentheses to change the order of operations. - If the evaluation is successful, a sequence of SQL/JSON items - (SQL/JSON sequence) is produced, - and the evaluation result is returned to the JSON query function - that completes the specified computation. + The standard comparison operators shown in are available for + jsonb, but not for json. They follow the + ordering rules for B-tree operations outlined at . - - To refer to the JSON data to be queried (the - context item), use the $ sign - in the path expression. It can be followed by one or more - accessor operators, - which go down the JSON structure level by level to retrieve the - content of context item. Each operator that follows deals with the - result of the previous evaluation step. + Some further operators also exist only for jsonb, as shown + in . + Many of these operators can be indexed by + jsonb operator classes. For a full description of + jsonb containment and existence semantics, see . + describes how these operators can be used to effectively index + jsonb data. + + Additional <type>jsonb</type> Operators + + + + Operator + Right Operand Type + Description + Example + + + + + @> + jsonb + Does the left JSON value contain the right JSON + path/value entries at the top level? + '{"a":1, "b":2}'::jsonb @> '{"b":2}'::jsonb + + + <@ + jsonb + Are the left JSON path/value entries contained at the top level within + the right JSON value? + '{"b":2}'::jsonb <@ '{"a":1, "b":2}'::jsonb + + + ? + text + Does the string exist as a top-level + key within the JSON value? + '{"a":1, "b":2}'::jsonb ? 'b' + + + ?| + text[] + Do any of these array strings + exist as top-level keys? + '{"a":1, "b":2, "c":3}'::jsonb ?| array['b', 'c'] + + + ?& + text[] + Do all of these array strings exist + as top-level keys? + '["a", "b"]'::jsonb ?& array['a', 'b'] + + + || + jsonb + Concatenate two jsonb values into a new jsonb value + '["a", "b"]'::jsonb || '["c", "d"]'::jsonb + + + - + text + Delete key/value pair or string + element from left operand. Key/value pairs are matched based + on their key value. + '{"a": "b"}'::jsonb - 'a' + + + - + text[] + Delete multiple key/value pairs or string + elements from left operand. Key/value pairs are matched based + on their key value. + '{"a": "b", "c": "d"}'::jsonb - '{a,c}'::text[] + + + - + integer + Delete the array element with specified index (Negative + integers count from the end). Throws an error if top level + container is not an array. + '["a", "b"]'::jsonb - 1 + + + #- + text[] + Delete the field or element with specified path (for + JSON arrays, negative integers count from the end) + '["a", {"b":1}]'::jsonb #- '{1,b}' + + + @? + jsonpath + Does JSON path return any item for the specified JSON value? + '{"a":[1,2,3,4,5]}'::jsonb @? '$.a[*] ? (@ > 2)' + + + @@ + jsonpath + Returns the result of JSON path predicate check for the specified JSON value. + Only the first item of the result is taken into account. If the + result is not Boolean, then null is returned. + '{"a":[1,2,3,4,5]}'::jsonb @@ '$.a[*] > 2' + + + +

- - For example, suppose you have some JSON data from a GPS tracker that you - would like to parse, such as: - -{ "track" : - { - "segments" : [ - { "location": [ 47.763, 13.4034 ], - "start time": "2018-10-14 10:05:14", - "HR": 73 - }, - { "location": [ 47.706, 13.2635 ], - "start time": "2018-10-14 10:39:21", - "HR": 135 - } ] - } -} - - - - - To retrieve the available track segments, you need to use the - .key accessor - operator for all the preceding JSON objects: - -'$.track.segments' - - - - - If the item to retrieve is an element of an array, you have - to unnest this array using the [*] operator. For example, - the following path will return location coordinates for all - the available track segments: - -'$.track.segments[*].location' - - + + + The || operator concatenates the elements at the top level of + each of its operands. It does not operate recursively. For example, if + both operands are objects with a common key field name, the value of the + field in the result will just be the value from the right hand operand. + + - - To return the coordinates of the first segment only, you can - specify the corresponding subscript in the [] - accessor operator. Note that the SQL/JSON arrays are 0-relative: - -'$.track.segments[0].location' - - + + + The @? and @@ operators suppress + the following errors: lacking object field or array element, unexpected + JSON item type, and numeric errors. + This behavior might be helpful while searching over JSON document + collections of varying structure. + + - The result of each path evaluation step can be processed - by one or more jsonpath operators and methods - listed in . - Each method name must be preceded by a dot. For example, - you can get an array size: - -'$.track.segments.size()' - - For more examples of using jsonpath operators - and methods within path expressions, see - . + shows the functions that are + available for creating json and jsonb values. + (There are no equivalent functions for jsonb, of the row_to_json + and array_to_json functions. However, the to_jsonb + function supplies much the same functionality as these functions would.) - - When defining the path, you can also use one or more - filter expressions that work similar to the - WHERE clause in SQL. A filter expression begins with - a question mark and provides a condition in parentheses: + + to_json + + + array_to_json + + + row_to_json + + + json_build_array + + + json_build_object + + + json_object + + + to_jsonb + + + jsonb_build_array + + + jsonb_build_object + + + jsonb_object + - -? (condition) - - + + JSON Creation Functions + + + + Function + Description + Example + Example Result + + + + + to_json(anyelement) + to_jsonb(anyelement) + + + Returns the value as json or jsonb. + Arrays and composites are converted + (recursively) to arrays and objects; otherwise, if there is a cast + from the type to json, the cast function will be used to + perform the conversion; otherwise, a scalar value is produced. + For any scalar type other than a number, a Boolean, or a null value, + the text representation will be used, in such a fashion that it is a + valid json or jsonb value. + + to_json('Fred said "Hi."'::text) + "Fred said \"Hi.\"" + + + + array_to_json(anyarray [, pretty_bool]) + + + Returns the array as a JSON array. A PostgreSQL multidimensional array + becomes a JSON array of arrays. Line feeds will be added between + dimension-1 elements if pretty_bool is true. + + array_to_json('{{1,5},{99,100}}'::int[]) + [[1,5],[99,100]] + + + + row_to_json(record [, pretty_bool]) + + + Returns the row as a JSON object. Line feeds will be added between + level-1 elements if pretty_bool is true. + + row_to_json(row(1,'foo')) + {"f1":1,"f2":"foo"} + + + json_build_array(VARIADIC "any") + jsonb_build_array(VARIADIC "any") + + + Builds a possibly-heterogeneously-typed JSON array out of a variadic + argument list. + + json_build_array(1,2,'3',4,5) + [1, 2, "3", 4, 5] + + + json_build_object(VARIADIC "any") + jsonb_build_object(VARIADIC "any") + + + Builds a JSON object out of a variadic argument list. By + convention, the argument list consists of alternating + keys and values. + + json_build_object('foo',1,'bar',2) + {"foo": 1, "bar": 2} + + + json_object(text[]) + jsonb_object(text[]) + + + Builds a JSON object out of a text array. The array must have either + exactly one dimension with an even number of members, in which case + they are taken as alternating key/value pairs, or two dimensions + such that each inner array has exactly two elements, which + are taken as a key/value pair. + + json_object('{a, 1, b, "def", c, 3.5}') + json_object('{{a, 1},{b, "def"},{c, 3.5}}') + {"a": "1", "b": "def", "c": "3.5"} + + + json_object(keys text[], values text[]) + jsonb_object(keys text[], values text[]) + + + This form of json_object takes keys and values pairwise from two separate + arrays. In all other respects it is identical to the one-argument form. + + json_object('{a, b}', '{1,2}') + {"a": "1", "b": "2"} + + + +

- - Filter expressions must be specified right after the path evaluation step - to which they are applied. The result of this step is filtered to include - only those items that satisfy the provided condition. SQL/JSON defines - three-valued logic, so the condition can be true, false, - or unknown. The unknown value - plays the same role as SQL NULL and can be tested - for with the is unknown predicate. Further path - evaluation steps use only those items for which filter expressions - return true. - + + + array_to_json and row_to_json have the same + behavior as to_json except for offering a pretty-printing + option. The behavior described for to_json likewise applies + to each individual value converted by the other JSON creation functions. + + - - Functions and operators that can be used in filter expressions are listed - in . The path - evaluation result to be filtered is denoted by the @ - variable. To refer to a JSON element stored at a lower nesting level, - add one or more accessor operators after @. - + + + The extension has a cast + from hstore to json, so that + hstore values converted via the JSON creation functions + will be represented as JSON objects, not as primitive string values. + + - Suppose you would like to retrieve all heart rate values higher - than 130. You can achieve this using the following expression: - -'$.track.segments[*].HR ? (@ > 130)' - + shows the functions that + are available for processing json and jsonb values. - - To get the start time of segments with such values instead, you have to - filter out irrelevant segments before returning the start time, so the - filter expression is applied to the previous step, and the path used - in the condition is different: + + json_array_length + + + jsonb_array_length + + + json_each + + + jsonb_each + + + json_each_text + + + jsonb_each_text + + + json_extract_path + + + jsonb_extract_path + + + json_extract_path_text + + + jsonb_extract_path_text + + + json_object_keys + + + jsonb_object_keys + + + json_populate_record + + + jsonb_populate_record + + + json_populate_recordset + + + jsonb_populate_recordset + + + json_array_elements + + + jsonb_array_elements + + + json_array_elements_text + + + jsonb_array_elements_text + + + json_typeof + + + jsonb_typeof + + + json_to_record + + + jsonb_to_record + + + json_to_recordset + + + jsonb_to_recordset + + + json_strip_nulls + + + jsonb_strip_nulls + + + jsonb_set + + + jsonb_insert + + + jsonb_pretty + + + jsonb_path_exists + + + jsonb_path_match + + + jsonb_path_query + + + jsonb_path_query_array + + + jsonb_path_query_first + + + + JSON Processing Functions + + + + Function + Return Type + Description + Example + Example Result + + + + + json_array_length(json) + jsonb_array_length(jsonb) + + int + + Returns the number of elements in the outermost JSON array. + + json_array_length('[1,2,3,{"f1":1,"f2":[5,6]},4]') + 5 + + + json_each(json) + jsonb_each(jsonb) + + setof key text, value json + setof key text, value jsonb + + + Expands the outermost JSON object into a set of key/value pairs. + + select * from json_each('{"a":"foo", "b":"bar"}') + -'$.track.segments[*] ? (@.HR > 130)."start time"' + key | value +-----+------- + a | "foo" + b | "bar" - - - - You can use several filter expressions on the same nesting level, if - required. For example, the following expression selects all segments - that contain locations with relevant coordinates and high heart rate values: + + + + json_each_text(json) + jsonb_each_text(jsonb) + + setof key text, value text + + Expands the outermost JSON object into a set of key/value pairs. The + returned values will be of type text. + + select * from json_each_text('{"a":"foo", "b":"bar"}') + -'$.track.segments[*] ? (@.location[1] < 13.4) ? (@.HR > 130)."start time"' + key | value +-----+------- + a | foo + b | bar - - - - Using filter expressions at different nesting levels is also allowed. - The following example first filters all segments by location, and then - returns high heart rate values for these segments, if available: + + + + json_extract_path(from_json json, VARIADIC path_elems text[]) + jsonb_extract_path(from_json jsonb, VARIADIC path_elems text[]) + + jsonjsonb + + + Returns JSON value pointed to by path_elems + (equivalent to #> operator). + + json_extract_path('{"f2":{"f3":1},"f4":{"f5":99,"f6":"foo"}}','f4') + {"f5":99,"f6":"foo"} + + + json_extract_path_text(from_json json, VARIADIC path_elems text[]) + jsonb_extract_path_text(from_json jsonb, VARIADIC path_elems text[]) + + text + + Returns JSON value pointed to by path_elems + as text + (equivalent to #>> operator). + + json_extract_path_text('{"f2":{"f3":1},"f4":{"f5":99,"f6":"foo"}}','f4', 'f6') + foo + + + json_object_keys(json) + jsonb_object_keys(jsonb) + + setof text + + Returns set of keys in the outermost JSON object. + + json_object_keys('{"f1":"abc","f2":{"f3":"a", "f4":"b"}}') + -'$.track.segments[*] ? (@.location[1] < 13.4).HR ? (@ > 130)' + json_object_keys +------------------ + f1 + f2 - - - - You can also nest filter expressions within each other: + + + + json_populate_record(base anyelement, from_json json) + jsonb_populate_record(base anyelement, from_json jsonb) + + anyelement + + Expands the object in from_json to a row + whose columns match the record type defined by base + (see note below). + + select * from json_populate_record(null::myrowtype, '{"a": 1, "b": ["2", "a b"], "c": {"d": 4, "e": "a b c"}}') + -'$.track ? (exists(@.segments[*] ? (@.HR > 130))).segments.size()' + a | b | c +---+-----------+------------- + 1 | {2,"a b"} | (4,"a b c") - This expression returns the size of the track if it contains any - segments with high heart rate values, or an empty sequence otherwise. - - - - PostgreSQL's implementation of SQL/JSON path - language has the following deviations from the SQL/JSON standard: - - - - - - .datetime() item method is not implemented yet - mainly because immutable jsonpath functions and operators - cannot reference session timezone, which is used in some datetime - operations. Datetime support will be added to jsonpath - in future versions of PostgreSQL. - - - - - - A path expression can be a Boolean predicate, although the SQL/JSON - standard allows predicates only in filters. This is necessary for - implementation of the @@ operator. For example, - the following jsonpath expression is valid in - PostgreSQL: + + + + json_populate_recordset(base anyelement, from_json json) + jsonb_populate_recordset(base anyelement, from_json jsonb) + + setof anyelement + + Expands the outermost array of objects + in from_json to a set of rows whose + columns match the record type defined by base (see + note below). + + select * from json_populate_recordset(null::myrowtype, '[{"a":1,"b":2},{"a":3,"b":4}]') + -'$.track.segments[*].HR < 70' + a | b +---+--- + 1 | 2 + 3 | 4 - - - - - - There are minor differences in the interpretation of regular - expression patterns used in like_regex filters, as - described in . - - - - - - Strict and Lax Modes - - When you query JSON data, the path expression may not match the - actual JSON data structure. An attempt to access a non-existent - member of an object or element of an array results in a - structural error. SQL/JSON path expressions have two modes - of handling structural errors: - - - - - - lax (default) — the path engine implicitly adapts - the queried data to the specified path. - Any remaining structural errors are suppressed and converted - to empty SQL/JSON sequences. - - - - - strict — if a structural error occurs, an error is raised. - - - - - - The lax mode facilitates matching of a JSON document structure and path - expression if the JSON data does not conform to the expected schema. - If an operand does not match the requirements of a particular operation, - it can be automatically wrapped as an SQL/JSON array or unwrapped by - converting its elements into an SQL/JSON sequence before performing - this operation. Besides, comparison operators automatically unwrap their - operands in the lax mode, so you can compare SQL/JSON arrays - out-of-the-box. An array of size 1 is considered equal to its sole element. - Automatic unwrapping is not performed only when: - - - - The path expression contains type() or - size() methods that return the type - and the number of elements in the array, respectively. - - - - - The queried JSON data contain nested arrays. In this case, only - the outermost array is unwrapped, while all the inner arrays - remain unchanged. Thus, implicit unwrapping can only go one - level down within each path evaluation step. - - - - - - - For example, when querying the GPS data listed above, you can - abstract from the fact that it stores an array of segments - when using the lax mode: + + + + json_array_elements(json) + jsonb_array_elements(jsonb) + + setof json + setof jsonb + + + Expands a JSON array to a set of JSON values. + + select * from json_array_elements('[1,true, [2,false]]') + -'lax $.track.segments.location' + value +----------- + 1 + true + [2,false] - - - - In the strict mode, the specified path must exactly match the structure of - the queried JSON document to return an SQL/JSON item, so using this - path expression will cause an error. To get the same result as in - the lax mode, you have to explicitly unwrap the - segments array: + + + + json_array_elements_text(json) + jsonb_array_elements_text(jsonb) + + setof text + + Expands a JSON array to a set of text values. + + select * from json_array_elements_text('["foo", "bar"]') + -'strict $.track.segments[*].location' + value +----------- + foo + bar - - - - - - Regular Expressions - - - LIKE_REGEX - in SQL/JSON - - - - SQL/JSON path expressions allow matching text to a regular expression - with the like_regex filter. For example, the - following SQL/JSON path query would case-insensitively match all - strings in an array that start with an English vowel: + + + + json_typeof(json) + jsonb_typeof(jsonb) + + text + + Returns the type of the outermost JSON value as a text string. + Possible types are + object, array, string, number, + boolean, and null. + + json_typeof('-123.4') + number + + + json_to_record(json) + jsonb_to_record(jsonb) + + record + + Builds an arbitrary record from a JSON object (see note below). As + with all functions returning record, the caller must + explicitly define the structure of the record with an AS + clause. + + select * from json_to_record('{"a":1,"b":[1,2,3],"c":[1,2,3],"e":"bar","r": {"a": 123, "b": "a b c"}}') as x(a int, b text, c int[], d text, r myrowtype) + -'$[*] ? (@ like_regex "^[aeiou]" flag "i")' + a | b | c | d | r +---+---------+---------+---+--------------- + 1 | [1,2,3] | {1,2,3} | | (123,"a b c") - - - - The optional flag string may include one or more of - the characters - i for case-insensitive match, - m to allow ^ - and $ to match at newlines, - s to allow . to match a newline, - and q to quote the whole pattern (reducing the - behavior to a simple substring match). - - - - The SQL/JSON standard borrows its definition for regular expressions - from the LIKE_REGEX operator, which in turn uses the - XQuery standard. PostgreSQL does not currently support the - LIKE_REGEX operator. Therefore, - the like_regex filter is implemented using the - POSIX regular expression engine described in - . This leads to various minor - discrepancies from standard SQL/JSON behavior, which are cataloged in - . - Note, however, that the flag-letter incompatibilities described there - do not apply to SQL/JSON, as it translates the XQuery flag letters to - match what the POSIX engine expects. - - - - Keep in mind that the pattern argument of like_regex - is a JSON path string literal, written according to the rules given in - . This means in particular that any - backslashes you want to use in the regular expression must be doubled. - For example, to match strings that contain only digits: + + + + json_to_recordset(json) + jsonb_to_recordset(jsonb) + + setof record + + Builds an arbitrary set of records from a JSON array of objects (see + note below). As with all functions returning record, the + caller must explicitly define the structure of the record with + an AS clause. + + select * from json_to_recordset('[{"a":1,"b":"foo"},{"a":"2","c":"bar"}]') as x(a int, b text); + -'$ ? (@ like_regex "^\\d+$")' - - - - - - - SQL/JSON Path Operators and Methods - - - shows the operators and - methods available in jsonpath. shows the available filter - expression elements. - - -

- <type>jsonpath</type> Operators and Methods - - - - Operator/Method - Description - Example JSON - Example Query - Result - - - - - + (unary) - Plus operator that iterates over the SQL/JSON sequence - {"x": [2.85, -14.7, -9.4]} - + $.x.floor() - 2, -15, -10 - - - - (unary) - Minus operator that iterates over the SQL/JSON sequence - {"x": [2.85, -14.7, -9.4]} - - $.x.floor() - -2, 15, 10 + a | b +---+----- + 1 | foo + 2 | + + + + + json_strip_nulls(from_json json) + jsonb_strip_nulls(from_json jsonb) + + jsonjsonb + + Returns from_json + with all object fields that have null values omitted. Other null values + are untouched. + + json_strip_nulls('[{"f1":1,"f2":null},2,null,3]') + [{"f1":1},2,null,3] - - + (binary) - Addition - [2] - 2 + $[0] - 4 + + jsonb_set(target jsonb, path text[], new_value jsonb, create_missing boolean) + + jsonb + + Returns target + with the section designated by path + replaced by new_value, or with + new_value added if + create_missing is true ( default is + true) and the item + designated by path does not exist. + As with the path orientated operators, negative integers that + appear in path count from the end + of JSON arrays. + + jsonb_set('[{"f1":1,"f2":null},2,null,3]', '{0,f1}','[2,3,4]', false) + jsonb_set('[{"f1":1,"f2":null},2]', '{0,f3}','[2,3,4]') + + [{"f1":[2,3,4],"f2":null},2,null,3] + [{"f1": 1, "f2": null, "f3": [2, 3, 4]}, 2] + - - - (binary) - Subtraction - [2] - 4 - $[0] - 2 + + + + jsonb_insert(target jsonb, path text[], new_value jsonb, insert_after boolean) + + + jsonb + + Returns target with + new_value inserted. If + target section designated by + path is in a JSONB array, + new_value will be inserted before target or + after if insert_after is true (default is + false). If target section + designated by path is in JSONB object, + new_value will be inserted only if + target does not exist. As with the path + orientated operators, negative integers that appear in + path count from the end of JSON arrays. + + + + jsonb_insert('{"a": [0,1,2]}', '{a, 1}', '"new_value"') + + + jsonb_insert('{"a": [0,1,2]}', '{a, 1}', '"new_value"', true) + + + {"a": [0, "new_value", 1, 2]} + {"a": [0, 1, "new_value", 2]} + - - * - Multiplication - [4] - 2 * $[0] - 8 + + jsonb_pretty(from_json jsonb) + + text + + Returns from_json + as indented JSON text. + + jsonb_pretty('[{"f1":1,"f2":null},2,null,3]') + + +[ + { + "f1": 1, + "f2": null + }, + 2, + null, + 3 +] + + - / - Division - [8] - $[0] / 2 - 4 + + + jsonb_path_exists(target jsonb, path jsonpath [, vars jsonb [, silent bool]]) + + + boolean + + Checks whether JSON path returns any item for the specified JSON + value. + + + + jsonb_path_exists('{"a":[1,2,3,4,5]}', '$.a[*] ? (@ >= $min && @ <= $max)', '{"min":2,"max":4}') + + + + true + - % - Modulus - [32] - $[0] % 10 - 2 + + + jsonb_path_match(target jsonb, path jsonpath [, vars jsonb, silent bool]) + + + boolean + + Returns the result of JSON path predicate check for the specified JSON value. + Only the first item of the result is taken into account. If the + result is not Boolean, then null is returned. + + + + jsonb_path_match('{"a":[1,2,3,4,5]}', 'exists($.a[*] ? (@ >= $min && @ <= $max))', '{"min":2,"max":4}') + + + + true + - type() - Type of the SQL/JSON item - [1, "2", {}] - $[*].type() - "number", "string", "object" + + + jsonb_path_query(target jsonb, path jsonpath [, vars jsonb, silent bool]) + + + setof jsonb + + Gets all JSON items returned by JSON path for the specified JSON + value. + + + + select * from jsonb_path_query('{"a":[1,2,3,4,5]}', '$.a[*] ? (@ >= $min && @ <= $max)', '{"min":2,"max":4}'); + + + + + + jsonb_path_query +------------------ + 2 + 3 + 4 + + + - size() - Size of the SQL/JSON item - {"m": [11, 15]} - $.m.size() - 2 + + + jsonb_path_query_array(target jsonb, path jsonpath [, vars jsonb, silent bool]) + + + jsonb + + Gets all JSON items returned by JSON path for the specified JSON + value and wraps result into an array. + + + + jsonb_path_query_array('{"a":[1,2,3,4,5]}', '$.a[*] ? (@ >= $min && @ <= $max)', '{"min":2,"max":4}') + + + + [2, 3, 4] + - double() - Approximate floating-point number converted from an SQL/JSON number or a string - {"len": "1.9"} - $.len.double() * 2 - 3.8 - - - ceiling() - Nearest integer greater than or equal to the SQL/JSON number - {"h": 1.3} - $.h.ceiling() - 2 - - - floor() - Nearest integer less than or equal to the SQL/JSON number - {"h": 1.3} - $.h.floor() - 1 - - - abs() - Absolute value of the SQL/JSON number - {"z": -0.3} - $.z.abs() - 0.3 - - - keyvalue() - Sequence of object's key-value pairs represented as array of items - containing three fields ("key", - "value", and "id"). - "id" is a unique identifier of the object - key-value pair belongs to. + + jsonb_path_query_first(target jsonb, path jsonpath [, vars jsonb, silent bool]) + - {"x": "20", "y": 32} - $.keyvalue() - {"key": "x", "value": "20", "id": 0}, {"key": "y", "value": 32, "id": 0} - - - -

- - - <type>jsonpath</type> Filter Expression Elements - - - - Value/Predicate - Description - Example JSON - Example Query - Result - - - - - == - Equality operator - [1, 2, 1, 3] - $[*] ? (@ == 1) - 1, 1 - - - != - Non-equality operator - [1, 2, 1, 3] - $[*] ? (@ != 1) - 2, 3 - - - <> - Non-equality operator (same as !=) - [1, 2, 1, 3] - $[*] ? (@ <> 1) - 2, 3 - - - < - Less-than operator - [1, 2, 3] - $[*] ? (@ < 2) - 1 - - - <= - Less-than-or-equal-to operator - [1, 2, 3] - $[*] ? (@ <= 2) - 1, 2 - - - > - Greater-than operator - [1, 2, 3] - $[*] ? (@ > 2) - 3 - - - >= - Greater-than-or-equal-to operator - [1, 2, 3] - $[*] ? (@ >= 2) - 2, 3 - - - true - Value used to perform comparison with JSON true literal - [{"name": "John", "parent": false}, - {"name": "Chris", "parent": true}] - $[*] ? (@.parent == true) - {"name": "Chris", "parent": true} - - - false - Value used to perform comparison with JSON false literal - [{"name": "John", "parent": false}, - {"name": "Chris", "parent": true}] - $[*] ? (@.parent == false) - {"name": "John", "parent": false} - - - null - Value used to perform comparison with JSON null value - [{"name": "Mary", "job": null}, - {"name": "Michael", "job": "driver"}] - $[*] ? (@.job == null) .name - "Mary" - - - && - Boolean AND - [1, 3, 7] - $[*] ? (@ > 1 && @ < 5) - 3 - - - || - Boolean OR - [1, 3, 7] - $[*] ? (@ < 1 || @ > 5) - 7 - - - ! - Boolean NOT - [1, 3, 7] - $[*] ? (!(@ < 5)) - 7 - - - like_regex + jsonb - Tests whether the first operand matches the regular expression - given by the second operand, optionally with modifications - described by a string of flag characters (see - ) + Gets the first JSON item returned by JSON path for the specified JSON + value. Returns NULL on no results. + + + + jsonb_path_query_first('{"a":[1,2,3,4,5]}', '$.a[*] ? (@ >= $min && @ <= $max)', '{"min":2,"max":4}') + + + + 2 - ["abc", "abd", "aBdC", "abdacb", "babc"] - $[*] ? (@ like_regex "^ab.*c" flag "i") - "abc", "aBdC", "abdacb" - - - starts with - Tests whether the second operand is an initial substring of the first operand - ["John Smith", "Mary Stone", "Bob Johnson"] - $[*] ? (@ starts with "John") - "John Smith" - - - exists - Tests whether a path expression matches at least one SQL/JSON item - {"x": [1, 2], "y": [2, 4]} - strict $.* ? (exists (@ ? (@[*] > 2))) - 2, 4 - - - is unknown - Tests whether a Boolean condition is unknown - [-1, 2, 7, "infinity"] - $[*] ? ((@ > 0) is unknown) - "infinity" - - -

- - - - - - JSON Functions and Operators - - JSON - functions and operators - + + + - - shows the operators that - are available for use with JSON data types (see ). - - - - <type>json</type> and <type>jsonb</type> Operators - - - - Operator - Right Operand Type - Return type - Description - Example - Example Result - - - - - -> - int - json or jsonb - Get JSON array element (indexed from zero, negative - integers count from the end) - '[{"a":"foo"},{"b":"bar"},{"c":"baz"}]'::json->2 - {"c":"baz"} - - - -> - text - json or jsonb - Get JSON object field by key - '{"a": {"b":"foo"}}'::json->'a' - {"b":"foo"} - - - ->> - int - text - Get JSON array element as text - '[1,2,3]'::json->>2 - 3 - - - ->> - text - text - Get JSON object field as text - '{"a":1,"b":2}'::json->>'b' - 2 - - - #> - text[] - json or jsonb - Get JSON object at the specified path - '{"a": {"b":{"c": "foo"}}}'::json#>'{a,b}' - {"c": "foo"} - - - #>> - text[] - text - Get JSON object at the specified path as text - '{"a":[1,2,3],"b":[4,5,6]}'::json#>>'{a,2}' - 3 - - - -

+ + + Many of these functions and operators will convert Unicode escapes in + JSON strings to the appropriate single character. This is a non-issue + if the input is type jsonb, because the conversion was already + done; but for json input, this may result in throwing an error, + as noted in . + + - There are parallel variants of these operators for both the - json and jsonb types. - The field/element/path extraction operators - return the same type as their left-hand input (either json - or jsonb), except for those specified as - returning text, which coerce the value to text. - The field/element/path extraction operators return NULL, rather than - failing, if the JSON input does not have the right structure to match - the request; for example if no such element exists. The - field/element/path extraction operators that accept integer JSON - array subscripts all support negative subscripting from the end of - arrays. + The functions + json[b]_populate_record, + json[b]_populate_recordset, + json[b]_to_record and + json[b]_to_recordset + operate on a JSON object, or array of objects, and extract the values + associated with keys whose names match column names of the output row + type. + Object fields that do not correspond to any output column name are + ignored, and output columns that do not match any object field will be + filled with nulls. + To convert a JSON value to the SQL type of an output column, the + following rules are applied in sequence: + + + + A JSON null value is converted to a SQL null in all cases. + + + + + If the output column is of type json + or jsonb, the JSON value is just reproduced exactly. + + + + + If the output column is a composite (row) type, and the JSON value is + a JSON object, the fields of the object are converted to columns of + the output row type by recursive application of these rules. + + + + + Likewise, if the output column is an array type and the JSON value is + a JSON array, the elements of the JSON array are converted to elements + of the output array by recursive application of these rules. + + + + + Otherwise, if the JSON value is a string literal, the contents of the + string are fed to the input conversion function for the column's data + type. + + + + + Otherwise, the ordinary text representation of the JSON value is fed + to the input conversion function for the column's data type. + + + - - - The standard comparison operators shown in are available for - jsonb, but not for json. They follow the - ordering rules for B-tree operations outlined at . - - - Some further operators also exist only for jsonb, as shown - in . - Many of these operators can be indexed by - jsonb operator classes. For a full description of - jsonb containment and existence semantics, see . - describes how these operators can be used to effectively index - jsonb data. - - - Additional <type>jsonb</type> Operators - - - - Operator - Right Operand Type - Description - Example - - - - - @> - jsonb - Does the left JSON value contain the right JSON - path/value entries at the top level? - '{"a":1, "b":2}'::jsonb @> '{"b":2}'::jsonb - - - <@ - jsonb - Are the left JSON path/value entries contained at the top level within - the right JSON value? - '{"b":2}'::jsonb <@ '{"a":1, "b":2}'::jsonb - - - ? - text - Does the string exist as a top-level - key within the JSON value? - '{"a":1, "b":2}'::jsonb ? 'b' - - - ?| - text[] - Do any of these array strings - exist as top-level keys? - '{"a":1, "b":2, "c":3}'::jsonb ?| array['b', 'c'] - - - ?& - text[] - Do all of these array strings exist - as top-level keys? - '["a", "b"]'::jsonb ?& array['a', 'b'] - - - || - jsonb - Concatenate two jsonb values into a new jsonb value - '["a", "b"]'::jsonb || '["c", "d"]'::jsonb - - - - - text - Delete key/value pair or string - element from left operand. Key/value pairs are matched based - on their key value. - '{"a": "b"}'::jsonb - 'a' - - - - - text[] - Delete multiple key/value pairs or string - elements from left operand. Key/value pairs are matched based - on their key value. - '{"a": "b", "c": "d"}'::jsonb - '{a,c}'::text[] - - - - - integer - Delete the array element with specified index (Negative - integers count from the end). Throws an error if top level - container is not an array. - '["a", "b"]'::jsonb - 1 - - - #- - text[] - Delete the field or element with specified path (for - JSON arrays, negative integers count from the end) - '["a", {"b":1}]'::jsonb #- '{1,b}' - - - @? - jsonpath - Does JSON path return any item for the specified JSON value? - '{"a":[1,2,3,4,5]}'::jsonb @? '$.a[*] ? (@ > 2)' - - - @@ - jsonpath - Returns the result of JSON path predicate check for the specified JSON value. - Only the first item of the result is taken into account. If the - result is not Boolean, then null is returned. - '{"a":[1,2,3,4,5]}'::jsonb @@ '$.a[*] > 2' - - - -

- - The || operator concatenates the elements at the top level of - each of its operands. It does not operate recursively. For example, if - both operands are objects with a common key field name, the value of the - field in the result will just be the value from the right hand operand. + While the examples for these functions use constants, the typical use + would be to reference a table in the FROM clause + and use one of its json or jsonb columns + as an argument to the function. Extracted key values can then be + referenced in other parts of the query, like WHERE + clauses and target lists. Extracting multiple values in this + way can improve performance over extracting them separately with + per-key operators. - - The @? and @@ operators suppress - the following errors: lacking object field or array element, unexpected - JSON item type, and numeric errors. - This behavior might be helpful while searching over JSON document - collections of varying structure. - + + All the items of the path parameter of jsonb_set + as well as jsonb_insert except the last item must be present + in the target. If create_missing is false, all + items of the path parameter of jsonb_set must be + present. If these conditions are not met the target is + returned unchanged. + + + If the last path item is an object key, it will be created if it + is absent and given the new value. If the last path item is an array + index, if it is positive the item to set is found by counting from + the left, and if negative by counting from the right - -1 + designates the rightmost element, and so on. + If the item is out of the range -array_length .. array_length -1, + and create_missing is true, the new value is added at the beginning + of the array if the item is negative, and at the end of the array if + it is positive. + - - shows the functions that are - available for creating json and jsonb values. - (There are no equivalent functions for jsonb, of the row_to_json - and array_to_json functions. However, the to_jsonb - function supplies much the same functionality as these functions would.) - - - - to_json - - - array_to_json - - - row_to_json - - - json_build_array - - - json_build_object - - - json_object - - - to_jsonb - - - jsonb_build_array - - - jsonb_build_object - - - jsonb_object - - - - JSON Creation Functions - - - - Function - Description - Example - Example Result - - - - - to_json(anyelement) - to_jsonb(anyelement) - - - Returns the value as json or jsonb. - Arrays and composites are converted - (recursively) to arrays and objects; otherwise, if there is a cast - from the type to json, the cast function will be used to - perform the conversion; otherwise, a scalar value is produced. - For any scalar type other than a number, a Boolean, or a null value, - the text representation will be used, in such a fashion that it is a - valid json or jsonb value. - - to_json('Fred said "Hi."'::text) - "Fred said \"Hi.\"" - - - - array_to_json(anyarray [, pretty_bool]) - - - Returns the array as a JSON array. A PostgreSQL multidimensional array - becomes a JSON array of arrays. Line feeds will be added between - dimension-1 elements if pretty_bool is true. - - array_to_json('{{1,5},{99,100}}'::int[]) - [[1,5],[99,100]] - - - - row_to_json(record [, pretty_bool]) - - - Returns the row as a JSON object. Line feeds will be added between - level-1 elements if pretty_bool is true. - - row_to_json(row(1,'foo')) - {"f1":1,"f2":"foo"} - - - json_build_array(VARIADIC "any") - jsonb_build_array(VARIADIC "any") - - - Builds a possibly-heterogeneously-typed JSON array out of a variadic - argument list. - - json_build_array(1,2,'3',4,5) - [1, 2, "3", 4, 5] - - - json_build_object(VARIADIC "any") - jsonb_build_object(VARIADIC "any") - - - Builds a JSON object out of a variadic argument list. By - convention, the argument list consists of alternating - keys and values. - - json_build_object('foo',1,'bar',2) - {"foo": 1, "bar": 2} - - - json_object(text[]) - jsonb_object(text[]) - - - Builds a JSON object out of a text array. The array must have either - exactly one dimension with an even number of members, in which case - they are taken as alternating key/value pairs, or two dimensions - such that each inner array has exactly two elements, which - are taken as a key/value pair. - - json_object('{a, 1, b, "def", c, 3.5}') - json_object('{{a, 1},{b, "def"},{c, 3.5}}') - {"a": "1", "b": "def", "c": "3.5"} - - - json_object(keys text[], values text[]) - jsonb_object(keys text[], values text[]) - - - This form of json_object takes keys and values pairwise from two separate - arrays. In all other respects it is identical to the one-argument form. - - json_object('{a, b}', '{1,2}') - {"a": "1", "b": "2"} - - - -

- - array_to_json and row_to_json have the same - behavior as to_json except for offering a pretty-printing - option. The behavior described for to_json likewise applies - to each individual value converted by the other JSON creation functions. + The json_typeof function's null return value + should not be confused with a SQL NULL. While + calling json_typeof('null'::json) will + return null, calling json_typeof(NULL::json) + will return a SQL NULL. - The extension has a cast - from hstore to json, so that - hstore values converted via the JSON creation functions - will be represented as JSON objects, not as primitive string values. + If the argument to json_strip_nulls contains duplicate + field names in any object, the result could be semantically somewhat + different, depending on the order in which they occur. This is not an + issue for jsonb_strip_nulls since jsonb values never have + duplicate object field names. + + + The jsonb_path_exists, jsonb_path_match, + jsonb_path_query, jsonb_path_query_array, and + jsonb_path_query_first + functions have optional vars and silent + arguments. + + + If the vars argument is specified, it provides an + object containing named variables to be substituted into a + jsonpath expression. + + + If the silent argument is specified and has the + true value, these functions suppress the same errors + as the @? and @@ operators. + + + - shows the functions that - are available for processing json and jsonb values. + See also for the aggregate + function json_agg which aggregates record + values as JSON, and the aggregate function + json_object_agg which aggregates pairs of values + into a JSON object, and their jsonb equivalents, + jsonb_agg and jsonb_object_agg. - - json_array_length - - - jsonb_array_length - - - json_each - - - jsonb_each - - - json_each_text - - - jsonb_each_text - - - json_extract_path - - - jsonb_extract_path - - - json_extract_path_text - - - jsonb_extract_path_text - - - json_object_keys - - - jsonb_object_keys - - - json_populate_record - - - jsonb_populate_record - - - json_populate_recordset - - - jsonb_populate_recordset - - - json_array_elements - - - jsonb_array_elements - - - json_array_elements_text - - - jsonb_array_elements_text - - - json_typeof - - - jsonb_typeof - - - json_to_record - - - jsonb_to_record - - - json_to_recordset - - - jsonb_to_recordset - - - json_strip_nulls - - - jsonb_strip_nulls - - - jsonb_set - - - jsonb_insert - - - jsonb_pretty - - - jsonb_path_exists - - - jsonb_path_match - - - jsonb_path_query - - - jsonb_path_query_array - - - jsonb_path_query_first + + + + SQL/JSON Path Expressions + + SQL/JSON + path expressions - - JSON Processing Functions - - - - Function - Return Type - Description - Example - Example Result - - - - - json_array_length(json) - jsonb_array_length(jsonb) - - int - - Returns the number of elements in the outermost JSON array. - - json_array_length('[1,2,3,{"f1":1,"f2":[5,6]},4]') - 5 - - - json_each(json) - jsonb_each(jsonb) - - setof key text, value json - setof key text, value jsonb - - - Expands the outermost JSON object into a set of key/value pairs. - - select * from json_each('{"a":"foo", "b":"bar"}') - + + SQL/JSON path expressions specify the items to be retrieved + from the JSON data, similar to XPath expressions used + for SQL access to XML. In PostgreSQL, + path expressions are implemented as the jsonpath + data type and can use any elements described in + . + + + JSON query functions and operators + pass the provided path expression to the path engine + for evaluation. If the expression matches the queried JSON data, + the corresponding SQL/JSON item is returned. + Path expressions are written in the SQL/JSON path language + and can also include arithmetic expressions and functions. + Query functions treat the provided expression as a + text string, so it must be enclosed in single quotes. + + + + A path expression consists of a sequence of elements allowed + by the jsonpath data type. + The path expression is evaluated from left to right, but + you can use parentheses to change the order of operations. + If the evaluation is successful, a sequence of SQL/JSON items + (SQL/JSON sequence) is produced, + and the evaluation result is returned to the JSON query function + that completes the specified computation. + + + + To refer to the JSON data to be queried (the + context item), use the $ sign + in the path expression. It can be followed by one or more + accessor operators, + which go down the JSON structure level by level to retrieve the + content of context item. Each operator that follows deals with the + result of the previous evaluation step. + + + + For example, suppose you have some JSON data from a GPS tracker that you + would like to parse, such as: + +{ "track" : + { + "segments" : [ + { "location": [ 47.763, 13.4034 ], + "start time": "2018-10-14 10:05:14", + "HR": 73 + }, + { "location": [ 47.706, 13.2635 ], + "start time": "2018-10-14 10:39:21", + "HR": 135 + } ] + } +} + + + + + To retrieve the available track segments, you need to use the + .key accessor + operator for all the preceding JSON objects: + +'$.track.segments' + + + + + If the item to retrieve is an element of an array, you have + to unnest this array using the [*] operator. For example, + the following path will return location coordinates for all + the available track segments: + +'$.track.segments[*].location' + + + + + To return the coordinates of the first segment only, you can + specify the corresponding subscript in the [] + accessor operator. Note that the SQL/JSON arrays are 0-relative: + +'$.track.segments[0].location' + + + + + The result of each path evaluation step can be processed + by one or more jsonpath operators and methods + listed in . + Each method name must be preceded by a dot. For example, + you can get an array size: + +'$.track.segments.size()' + + For more examples of using jsonpath operators + and methods within path expressions, see + . + + + + When defining the path, you can also use one or more + filter expressions that work similar to the + WHERE clause in SQL. A filter expression begins with + a question mark and provides a condition in parentheses: + + +? (condition) + + + + + Filter expressions must be specified right after the path evaluation step + to which they are applied. The result of this step is filtered to include + only those items that satisfy the provided condition. SQL/JSON defines + three-valued logic, so the condition can be true, false, + or unknown. The unknown value + plays the same role as SQL NULL and can be tested + for with the is unknown predicate. Further path + evaluation steps use only those items for which filter expressions + return true. + + + + Functions and operators that can be used in filter expressions are listed + in . The path + evaluation result to be filtered is denoted by the @ + variable. To refer to a JSON element stored at a lower nesting level, + add one or more accessor operators after @. + + + + Suppose you would like to retrieve all heart rate values higher + than 130. You can achieve this using the following expression: - key | value ------+------- - a | "foo" - b | "bar" +'$.track.segments[*].HR ? (@ > 130)' - - - - json_each_text(json) - jsonb_each_text(jsonb) - - setof key text, value text - - Expands the outermost JSON object into a set of key/value pairs. The - returned values will be of type text. - - select * from json_each_text('{"a":"foo", "b":"bar"}') - + + + + To get the start time of segments with such values instead, you have to + filter out irrelevant segments before returning the start time, so the + filter expression is applied to the previous step, and the path used + in the condition is different: - key | value ------+------- - a | foo - b | bar +'$.track.segments[*] ? (@.HR > 130)."start time"' - - - - json_extract_path(from_json json, VARIADIC path_elems text[]) - jsonb_extract_path(from_json jsonb, VARIADIC path_elems text[]) - - jsonjsonb - - - Returns JSON value pointed to by path_elems - (equivalent to #> operator). - - json_extract_path('{"f2":{"f3":1},"f4":{"f5":99,"f6":"foo"}}','f4') - {"f5":99,"f6":"foo"} - - - json_extract_path_text(from_json json, VARIADIC path_elems text[]) - jsonb_extract_path_text(from_json jsonb, VARIADIC path_elems text[]) - - text - - Returns JSON value pointed to by path_elems - as text - (equivalent to #>> operator). - - json_extract_path_text('{"f2":{"f3":1},"f4":{"f5":99,"f6":"foo"}}','f4', 'f6') - foo - - - json_object_keys(json) - jsonb_object_keys(jsonb) - - setof text - - Returns set of keys in the outermost JSON object. - - json_object_keys('{"f1":"abc","f2":{"f3":"a", "f4":"b"}}') - + + + + You can use several filter expressions on the same nesting level, if + required. For example, the following expression selects all segments + that contain locations with relevant coordinates and high heart rate values: - json_object_keys ------------------- - f1 - f2 +'$.track.segments[*] ? (@.location[1] < 13.4) ? (@.HR > 130)."start time"' - - - - json_populate_record(base anyelement, from_json json) - jsonb_populate_record(base anyelement, from_json jsonb) - - anyelement - - Expands the object in from_json to a row - whose columns match the record type defined by base - (see note below). - - select * from json_populate_record(null::myrowtype, '{"a": 1, "b": ["2", "a b"], "c": {"d": 4, "e": "a b c"}}') - + + + + Using filter expressions at different nesting levels is also allowed. + The following example first filters all segments by location, and then + returns high heart rate values for these segments, if available: - a | b | c ----+-----------+------------- - 1 | {2,"a b"} | (4,"a b c") +'$.track.segments[*] ? (@.location[1] < 13.4).HR ? (@ > 130)' - - - - json_populate_recordset(base anyelement, from_json json) - jsonb_populate_recordset(base anyelement, from_json jsonb) - - setof anyelement - - Expands the outermost array of objects - in from_json to a set of rows whose - columns match the record type defined by base (see - note below). - - select * from json_populate_recordset(null::myrowtype, '[{"a":1,"b":2},{"a":3,"b":4}]') - + + + + You can also nest filter expressions within each other: - a | b ----+--- - 1 | 2 - 3 | 4 +'$.track ? (exists(@.segments[*] ? (@.HR > 130))).segments.size()' - - - - json_array_elements(json) - jsonb_array_elements(jsonb) - - setof json - setof jsonb - - - Expands a JSON array to a set of JSON values. - - select * from json_array_elements('[1,true, [2,false]]') - + This expression returns the size of the track if it contains any + segments with high heart rate values, or an empty sequence otherwise. + + + + PostgreSQL's implementation of SQL/JSON path + language has the following deviations from the SQL/JSON standard: + + + + + + .datetime() item method is not implemented yet + mainly because immutable jsonpath functions and operators + cannot reference session timezone, which is used in some datetime + operations. Datetime support will be added to jsonpath + in future versions of PostgreSQL. + + + + + + A path expression can be a Boolean predicate, although the SQL/JSON + standard allows predicates only in filters. This is necessary for + implementation of the @@ operator. For example, + the following jsonpath expression is valid in + PostgreSQL: + +'$.track.segments[*].HR < 70' + + + + + + + There are minor differences in the interpretation of regular + expression patterns used in like_regex filters, as + described in . + + + + + + Strict and Lax Modes + + When you query JSON data, the path expression may not match the + actual JSON data structure. An attempt to access a non-existent + member of an object or element of an array results in a + structural error. SQL/JSON path expressions have two modes + of handling structural errors: + + + + + + lax (default) — the path engine implicitly adapts + the queried data to the specified path. + Any remaining structural errors are suppressed and converted + to empty SQL/JSON sequences. + + + + + strict — if a structural error occurs, an error is raised. + + + + + + The lax mode facilitates matching of a JSON document structure and path + expression if the JSON data does not conform to the expected schema. + If an operand does not match the requirements of a particular operation, + it can be automatically wrapped as an SQL/JSON array or unwrapped by + converting its elements into an SQL/JSON sequence before performing + this operation. Besides, comparison operators automatically unwrap their + operands in the lax mode, so you can compare SQL/JSON arrays + out-of-the-box. An array of size 1 is considered equal to its sole element. + Automatic unwrapping is not performed only when: + + + + The path expression contains type() or + size() methods that return the type + and the number of elements in the array, respectively. + + + + + The queried JSON data contain nested arrays. In this case, only + the outermost array is unwrapped, while all the inner arrays + remain unchanged. Thus, implicit unwrapping can only go one + level down within each path evaluation step. + + + + + + + For example, when querying the GPS data listed above, you can + abstract from the fact that it stores an array of segments + when using the lax mode: - value ------------ - 1 - true - [2,false] +'lax $.track.segments.location' - - - - json_array_elements_text(json) - jsonb_array_elements_text(jsonb) - - setof text - - Expands a JSON array to a set of text values. - - select * from json_array_elements_text('["foo", "bar"]') - + + + + In the strict mode, the specified path must exactly match the structure of + the queried JSON document to return an SQL/JSON item, so using this + path expression will cause an error. To get the same result as in + the lax mode, you have to explicitly unwrap the + segments array: - value ------------ - foo - bar +'strict $.track.segments[*].location' - - - - json_typeof(json) - jsonb_typeof(jsonb) - - text - - Returns the type of the outermost JSON value as a text string. - Possible types are - object, array, string, number, - boolean, and null. - - json_typeof('-123.4') - number - - - json_to_record(json) - jsonb_to_record(jsonb) - - record - - Builds an arbitrary record from a JSON object (see note below). As - with all functions returning record, the caller must - explicitly define the structure of the record with an AS - clause. - - select * from json_to_record('{"a":1,"b":[1,2,3],"c":[1,2,3],"e":"bar","r": {"a": 123, "b": "a b c"}}') as x(a int, b text, c int[], d text, r myrowtype) - + + + + + + Regular Expressions + + + LIKE_REGEX + in SQL/JSON + + + + SQL/JSON path expressions allow matching text to a regular expression + with the like_regex filter. For example, the + following SQL/JSON path query would case-insensitively match all + strings in an array that start with an English vowel: - a | b | c | d | r ----+---------+---------+---+--------------- - 1 | [1,2,3] | {1,2,3} | | (123,"a b c") +'$[*] ? (@ like_regex "^[aeiou]" flag "i")' - - - - json_to_recordset(json) - jsonb_to_recordset(jsonb) - - setof record - - Builds an arbitrary set of records from a JSON array of objects (see - note below). As with all functions returning record, the - caller must explicitly define the structure of the record with - an AS clause. - - select * from json_to_recordset('[{"a":1,"b":"foo"},{"a":"2","c":"bar"}]') as x(a int, b text); - + + + + The optional flag string may include one or more of + the characters + i for case-insensitive match, + m to allow ^ + and $ to match at newlines, + s to allow . to match a newline, + and q to quote the whole pattern (reducing the + behavior to a simple substring match). + + + + The SQL/JSON standard borrows its definition for regular expressions + from the LIKE_REGEX operator, which in turn uses the + XQuery standard. PostgreSQL does not currently support the + LIKE_REGEX operator. Therefore, + the like_regex filter is implemented using the + POSIX regular expression engine described in + . This leads to various minor + discrepancies from standard SQL/JSON behavior, which are cataloged in + . + Note, however, that the flag-letter incompatibilities described there + do not apply to SQL/JSON, as it translates the XQuery flag letters to + match what the POSIX engine expects. + + + + Keep in mind that the pattern argument of like_regex + is a JSON path string literal, written according to the rules given in + . This means in particular that any + backslashes you want to use in the regular expression must be doubled. + For example, to match strings that contain only digits: - a | b ----+----- - 1 | foo - 2 | +'$ ? (@ like_regex "^\\d+$")' - - - - json_strip_nulls(from_json json) - jsonb_strip_nulls(from_json jsonb) - - jsonjsonb - - Returns from_json - with all object fields that have null values omitted. Other null values - are untouched. - - json_strip_nulls('[{"f1":1,"f2":null},2,null,3]') - [{"f1":1},2,null,3] + + + + + + SQL/JSON Path Operators and Methods + + + shows the operators and + methods available in jsonpath. shows the available filter + expression elements. + + +

+ <type>jsonpath</type> Operators and Methods + + + + Operator/Method + Description + Example JSON + Example Query + Result + + + + + + (unary) + Plus operator that iterates over the SQL/JSON sequence + {"x": [2.85, -14.7, -9.4]} + + $.x.floor() + 2, -15, -10 + + + - (unary) + Minus operator that iterates over the SQL/JSON sequence + {"x": [2.85, -14.7, -9.4]} + - $.x.floor() + -2, 15, 10 + + + + (binary) + Addition + [2] + 2 + $[0] + 4 + + + - (binary) + Subtraction + [2] + 4 - $[0] + 2 + + + * + Multiplication + [4] + 2 * $[0] + 8 + + + / + Division + [8] + $[0] / 2 + 4 + + + % + Modulus + [32] + $[0] % 10 + 2 - - jsonb_set(target jsonb, path text[], new_value jsonb, create_missing boolean) - - jsonb - - Returns target - with the section designated by path - replaced by new_value, or with - new_value added if - create_missing is true ( default is - true) and the item - designated by path does not exist. - As with the path orientated operators, negative integers that - appear in path count from the end - of JSON arrays. - - jsonb_set('[{"f1":1,"f2":null},2,null,3]', '{0,f1}','[2,3,4]', false) - jsonb_set('[{"f1":1,"f2":null},2]', '{0,f3}','[2,3,4]') - - [{"f1":[2,3,4],"f2":null},2,null,3] - [{"f1": 1, "f2": null, "f3": [2, 3, 4]}, 2] - + + type() + Type of the SQL/JSON item + [1, "2", {}] + $[*].type() + "number", "string", "object" - - - - jsonb_insert(target jsonb, path text[], new_value jsonb, insert_after boolean) - - - jsonb - - Returns target with - new_value inserted. If - target section designated by - path is in a JSONB array, - new_value will be inserted before target or - after if insert_after is true (default is - false). If target section - designated by path is in JSONB object, - new_value will be inserted only if - target does not exist. As with the path - orientated operators, negative integers that appear in - path count from the end of JSON arrays. - - - - jsonb_insert('{"a": [0,1,2]}', '{a, 1}', '"new_value"') - - - jsonb_insert('{"a": [0,1,2]}', '{a, 1}', '"new_value"', true) - - - {"a": [0, "new_value", 1, 2]} - {"a": [0, 1, "new_value", 2]} - + + size() + Size of the SQL/JSON item + {"m": [11, 15]} + $.m.size() + 2 - - jsonb_pretty(from_json jsonb) - - text - - Returns from_json - as indented JSON text. - - jsonb_pretty('[{"f1":1,"f2":null},2,null,3]') - - -[ - { - "f1": 1, - "f2": null - }, - 2, - null, - 3 -] - - + + double() + Approximate floating-point number converted from an SQL/JSON number or a string + {"len": "1.9"} + $.len.double() * 2 + 3.8 - - - jsonb_path_exists(target jsonb, path jsonpath [, vars jsonb [, silent bool]]) - - - boolean - - Checks whether JSON path returns any item for the specified JSON - value. - - - - jsonb_path_exists('{"a":[1,2,3,4,5]}', '$.a[*] ? (@ >= $min && @ <= $max)', '{"min":2,"max":4}') - - - - true - + ceiling() + Nearest integer greater than or equal to the SQL/JSON number + {"h": 1.3} + $.h.ceiling() + 2 + floor() + Nearest integer less than or equal to the SQL/JSON number + {"h": 1.3} + $.h.floor() + 1 + + + abs() + Absolute value of the SQL/JSON number + {"z": -0.3} + $.z.abs() + 0.3 + + + keyvalue() - - jsonb_path_match(target jsonb, path jsonpath [, vars jsonb, silent bool]) - - - boolean - - Returns the result of JSON path predicate check for the specified JSON value. - Only the first item of the result is taken into account. If the - result is not Boolean, then null is returned. - - - - jsonb_path_match('{"a":[1,2,3,4,5]}', 'exists($.a[*] ? (@ >= $min && @ <= $max))', '{"min":2,"max":4}') - - - - true + Sequence of object's key-value pairs represented as array of items + containing three fields ("key", + "value", and "id"). + "id" is a unique identifier of the object + key-value pair belongs to. + {"x": "20", "y": 32} + $.keyvalue() + {"key": "x", "value": "20", "id": 0}, {"key": "y", "value": 32, "id": 0} + + + +

+ + + <type>jsonpath</type> Filter Expression Elements + + + + Value/Predicate + Description + Example JSON + Example Query + Result + + + + + == + Equality operator + [1, 2, 1, 3] + $[*] ? (@ == 1) + 1, 1 + + + != + Non-equality operator + [1, 2, 1, 3] + $[*] ? (@ != 1) + 2, 3 + + + <> + Non-equality operator (same as !=) + [1, 2, 1, 3] + $[*] ? (@ <> 1) + 2, 3 + + + < + Less-than operator + [1, 2, 3] + $[*] ? (@ < 2) + 1 + + + <= + Less-than-or-equal-to operator + [1, 2, 3] + $[*] ? (@ <= 2) + 1, 2 + + + > + Greater-than operator + [1, 2, 3] + $[*] ? (@ > 2) + 3 + + + >= + Greater-than-or-equal-to operator + [1, 2, 3] + $[*] ? (@ >= 2) + 2, 3 + + + true + Value used to perform comparison with JSON true literal + [{"name": "John", "parent": false}, + {"name": "Chris", "parent": true}] + $[*] ? (@.parent == true) + {"name": "Chris", "parent": true} + + + false + Value used to perform comparison with JSON false literal + [{"name": "John", "parent": false}, + {"name": "Chris", "parent": true}] + $[*] ? (@.parent == false) + {"name": "John", "parent": false} + + + null + Value used to perform comparison with JSON null value + [{"name": "Mary", "job": null}, + {"name": "Michael", "job": "driver"}] + $[*] ? (@.job == null) .name + "Mary" + + + && + Boolean AND + [1, 3, 7] + $[*] ? (@ > 1 && @ < 5) + 3 + + + || + Boolean OR + [1, 3, 7] + $[*] ? (@ < 1 || @ > 5) + 7 - - - jsonb_path_query(target jsonb, path jsonpath [, vars jsonb, silent bool]) - - - setof jsonb - - Gets all JSON items returned by JSON path for the specified JSON - value. - - - - select * from jsonb_path_query('{"a":[1,2,3,4,5]}', '$.a[*] ? (@ >= $min && @ <= $max)', '{"min":2,"max":4}'); - - - - - - jsonb_path_query ------------------- - 2 - 3 - 4 - - - + ! + Boolean NOT + [1, 3, 7] + $[*] ? (!(@ < 5)) + 7 + like_regex - - jsonb_path_query_array(target jsonb, path jsonpath [, vars jsonb, silent bool]) - - - jsonb - - Gets all JSON items returned by JSON path for the specified JSON - value and wraps result into an array. - - - - jsonb_path_query_array('{"a":[1,2,3,4,5]}', '$.a[*] ? (@ >= $min && @ <= $max)', '{"min":2,"max":4}') - - - - [2, 3, 4] + Tests whether the first operand matches the regular expression + given by the second operand, optionally with modifications + described by a string of flag characters (see + ) + ["abc", "abd", "aBdC", "abdacb", "babc"] + $[*] ? (@ like_regex "^ab.*c" flag "i") + "abc", "aBdC", "abdacb" - - - jsonb_path_query_first(target jsonb, path jsonpath [, vars jsonb, silent bool]) - - - jsonb - - Gets the first JSON item returned by JSON path for the specified JSON - value. Returns NULL on no results. - - - - jsonb_path_query_first('{"a":[1,2,3,4,5]}', '$.a[*] ? (@ >= $min && @ <= $max)', '{"min":2,"max":4}') - - - - 2 - + starts with + Tests whether the second operand is an initial substring of the first operand + ["John Smith", "Mary Stone", "Bob Johnson"] + $[*] ? (@ starts with "John") + "John Smith" - - -

- - - - Many of these functions and operators will convert Unicode escapes in - JSON strings to the appropriate single character. This is a non-issue - if the input is type jsonb, because the conversion was already - done; but for json input, this may result in throwing an error, - as noted in . - - - - - - The functions - json[b]_populate_record, - json[b]_populate_recordset, - json[b]_to_record and - json[b]_to_recordset - operate on a JSON object, or array of objects, and extract the values - associated with keys whose names match column names of the output row - type. - Object fields that do not correspond to any output column name are - ignored, and output columns that do not match any object field will be - filled with nulls. - To convert a JSON value to the SQL type of an output column, the - following rules are applied in sequence: - - - - A JSON null value is converted to a SQL null in all cases. - - - - - If the output column is of type json - or jsonb, the JSON value is just reproduced exactly. - - - - - If the output column is a composite (row) type, and the JSON value is - a JSON object, the fields of the object are converted to columns of - the output row type by recursive application of these rules. - - - - - Likewise, if the output column is an array type and the JSON value is - a JSON array, the elements of the JSON array are converted to elements - of the output array by recursive application of these rules. - - - - - Otherwise, if the JSON value is a string literal, the contents of the - string are fed to the input conversion function for the column's data - type. - - - - - Otherwise, the ordinary text representation of the JSON value is fed - to the input conversion function for the column's data type. - - - - - - - While the examples for these functions use constants, the typical use - would be to reference a table in the FROM clause - and use one of its json or jsonb columns - as an argument to the function. Extracted key values can then be - referenced in other parts of the query, like WHERE - clauses and target lists. Extracting multiple values in this - way can improve performance over extracting them separately with - per-key operators. - - - - - - All the items of the path parameter of jsonb_set - as well as jsonb_insert except the last item must be present - in the target. If create_missing is false, all - items of the path parameter of jsonb_set must be - present. If these conditions are not met the target is - returned unchanged. - - - If the last path item is an object key, it will be created if it - is absent and given the new value. If the last path item is an array - index, if it is positive the item to set is found by counting from - the left, and if negative by counting from the right - -1 - designates the rightmost element, and so on. - If the item is out of the range -array_length .. array_length -1, - and create_missing is true, the new value is added at the beginning - of the array if the item is negative, and at the end of the array if - it is positive. - - - - - - The json_typeof function's null return value - should not be confused with a SQL NULL. While - calling json_typeof('null'::json) will - return null, calling json_typeof(NULL::json) - will return a SQL NULL. - - - - - - If the argument to json_strip_nulls contains duplicate - field names in any object, the result could be semantically somewhat - different, depending on the order in which they occur. This is not an - issue for jsonb_strip_nulls since jsonb values never have - duplicate object field names. - - - - - - The jsonb_path_exists, jsonb_path_match, - jsonb_path_query, jsonb_path_query_array, and - jsonb_path_query_first - functions have optional vars and silent - arguments. - - - If the vars argument is specified, it provides an - object containing named variables to be substituted into a - jsonpath expression. - - - If the silent argument is specified and has the - true value, these functions suppress the same errors - as the @? and @@ operators. - - - - - See also for the aggregate - function json_agg which aggregates record - values as JSON, and the aggregate function - json_object_agg which aggregates pairs of values - into a JSON object, and their jsonb equivalents, - jsonb_agg and jsonb_object_agg. - + + exists + Tests whether a path expression matches at least one SQL/JSON item + {"x": [1, 2], "y": [2, 4]} + strict $.* ? (exists (@ ? (@[*] > 2))) + 2, 4 + + + is unknown + Tests whether a Boolean condition is unknown + [-1, 2, 7, "infinity"] + $[*] ? ((@ > 0) is unknown) + "infinity" + + + + + - + diff --git a/doc/src/sgml/json.sgml b/doc/src/sgml/json.sgml index 45b22b6e2d..6ff8751870 100644 --- a/doc/src/sgml/json.sgml +++ b/doc/src/sgml/json.sgml @@ -641,8 +641,7 @@ SELECT jdoc->'guid', jdoc->'name' FROM api WHERE jdoc @> '{"tags": ["qu - The SQL/JSON path language is fully integrated into the SQL engine: - the semantics of its predicates and operators generally follow SQL. + The semantics of SQL/JSON path predicates and operators generally follow SQL. At the same time, to provide a most natural way of working with JSON data, SQL/JSON path syntax uses some of the JavaScript conventions: --------------3479AF35BF75E785ECC268AB--