public inbox for [email protected]help / color / mirror / Atom feed
[PATCH v21 6/8] Row pattern recognition patch (docs). 4+ messages / 4 participants [nested] [flat]
* [PATCH v21 6/8] Row pattern recognition patch (docs). @ 2024-08-26 04:32 Tatsuo Ishii <[email protected]> 0 siblings, 0 replies; 4+ messages in thread From: Tatsuo Ishii @ 2024-08-26 04:32 UTC (permalink / raw) --- doc/src/sgml/advanced.sgml | 82 ++++++++++++++++++++++++++++++++++++ doc/src/sgml/func.sgml | 54 ++++++++++++++++++++++++ doc/src/sgml/ref/select.sgml | 38 ++++++++++++++++- 3 files changed, 172 insertions(+), 2 deletions(-) diff --git a/doc/src/sgml/advanced.sgml b/doc/src/sgml/advanced.sgml index 755c9f1485..b0b1d1c51e 100644 --- a/doc/src/sgml/advanced.sgml +++ b/doc/src/sgml/advanced.sgml @@ -537,6 +537,88 @@ WHERE pos < 3; <literal>rank</literal> less than 3. </para> + <para> + Row pattern common syntax can be used to perform row pattern recognition + in a query. The row pattern common syntax includes two sub + clauses: <literal>DEFINE</literal> + and <literal>PATTERN</literal>. <literal>DEFINE</literal> defines + definition variables along with an expression. The expression must be a + logical expression, which means it must + return <literal>TRUE</literal>, <literal>FALSE</literal> + or <literal>NULL</literal>. The expression may comprise column references + and functions. Window functions, aggregate functions and subqueries are + not allowed. An example of <literal>DEFINE</literal> is as follows. + +<programlisting> +DEFINE + LOWPRICE AS price <= 100, + UP AS price > PREV(price), + DOWN AS price < PREV(price) +</programlisting> + + Note that <function>PREV</function> returns the price column in the + previous row if it's called in a context of row pattern recognition. Thus in + the second line the definition variable "UP" is <literal>TRUE</literal> + when the price column in the current row is greater than the price column + in the previous row. Likewise, "DOWN" is <literal>TRUE</literal> when when + the price column in the current row is lower than the price column in the + previous row. + </para> + <para> + Once <literal>DEFINE</literal> exists, <literal>PATTERN</literal> can be + used. <literal>PATTERN</literal> defines a sequence of rows that satisfies + certain conditions. For example following <literal>PATTERN</literal> + defines that a row starts with the condition "LOWPRICE", then one or more + rows satisfy "UP" and finally one or more rows satisfy "DOWN". Note that + "+" means one or more matches. Also you can use "*", which means zero or + more matches. If a sequence of rows which satisfies the PATTERN is found, + in the starting row of the sequence of rows all window functions and + aggregates are shown in the target list. Note that aggregations only look + into the matched rows, rather than whole frame. On the second or + subsequent rows all window functions are NULL. Aggregates are NULL or 0 + (count case) depending on its aggregation definition. For rows that do not + match on the PATTERN, all window functions and aggregates are shown AS + NULL too, except count showing 0. This is because the rows do not match, + thus they are in an empty frame. Example of a <literal>SELECT</literal> + using the <literal>DEFINE</literal> and <literal>PATTERN</literal> clause + is as follows. + +<programlisting> +SELECT company, tdate, price, + first_value(price) OVER w, + max(price) OVER w, + count(price) OVER w +FROM stock + WINDOW w AS ( + PARTITION BY company + ORDER BY tdate + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + AFTER MATCH SKIP PAST LAST ROW + INITIAL + PATTERN (LOWPRICE UP+ DOWN+) + DEFINE + LOWPRICE AS price <= 100, + UP AS price > PREV(price), + DOWN AS price < PREV(price) +); +</programlisting> +<screen> + company | tdate | price | first_value | max | count +----------+------------+-------+-------------+-----+------- + company1 | 2023-07-01 | 100 | 100 | 200 | 4 + company1 | 2023-07-02 | 200 | | | 0 + company1 | 2023-07-03 | 150 | | | 0 + company1 | 2023-07-04 | 140 | | | 0 + company1 | 2023-07-05 | 150 | | | 0 + company1 | 2023-07-06 | 90 | 90 | 130 | 4 + company1 | 2023-07-07 | 110 | | | 0 + company1 | 2023-07-08 | 130 | | | 0 + company1 | 2023-07-09 | 120 | | | 0 + company1 | 2023-07-10 | 130 | | | 0 +(10 rows) +</screen> + </para> + <para> When a query involves multiple window functions, it is possible to write out each one with a separate <literal>OVER</literal> clause, but this is diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml index 461fc3f437..02ad2b0195 100644 --- a/doc/src/sgml/func.sgml +++ b/doc/src/sgml/func.sgml @@ -23258,6 +23258,7 @@ SELECT count(*) FROM sometable; returns <literal>NULL</literal> if there is no such row. </para></entry> </row> + </tbody> </tgroup> </table> @@ -23297,6 +23298,59 @@ SELECT count(*) FROM sometable; Other frame specifications can be used to obtain other effects. </para> + <para> + Row pattern recognition navigation functions are listed in + <xref linkend="functions-rpr-navigation-table"/>. These functions + can be used to describe DEFINE clause of Row pattern recognition. + </para> + + <table id="functions-rpr-navigation-table"> + <title>Row Pattern Navigation Functions</title> + <tgroup cols="1"> + <thead> + <row> + <entry role="func_table_entry"><para role="func_signature"> + Function + </para> + <para> + Description + </para></entry> + </row> + </thead> + + <tbody> + <row> + <entry role="func_table_entry"><para role="func_signature"> + <indexterm> + <primary>prev</primary> + </indexterm> + <function>prev</function> ( <parameter>value</parameter> <type>anyelement</type> ) + <returnvalue>anyelement</returnvalue> + </para> + <para> + Returns the column value at the previous row; + returns NULL if there is no previous row in the window frame. + </para></entry> + </row> + + <row> + <entry role="func_table_entry"><para role="func_signature"> + <indexterm> + <primary>next</primary> + </indexterm> + <function>next</function> ( <parameter>value</parameter> <type>anyelement</type> ) + <returnvalue>anyelement</returnvalue> + </para> + <para> + Returns the column value at the next row; + returns NULL if there is no next row in the window frame. + </para></entry> + </row> + + </tbody> + </tgroup> + </table> + <note> <para> The SQL standard defines a <literal>RESPECT NULLS</literal> or diff --git a/doc/src/sgml/ref/select.sgml b/doc/src/sgml/ref/select.sgml index d7089eac0b..7e1c9989ba 100644 --- a/doc/src/sgml/ref/select.sgml +++ b/doc/src/sgml/ref/select.sgml @@ -969,8 +969,8 @@ WINDOW <replaceable class="parameter">window_name</replaceable> AS ( <replaceabl The <replaceable class="parameter">frame_clause</replaceable> can be one of <synopsis> -{ RANGE | ROWS | GROUPS } <replaceable>frame_start</replaceable> [ <replaceable>frame_exclusion</replaceable> ] -{ RANGE | ROWS | GROUPS } BETWEEN <replaceable>frame_start</replaceable> AND <replaceable>frame_end</replaceable> [ <replaceable>frame_exclusion</replaceable> ] +{ RANGE | ROWS | GROUPS } <replaceable>frame_start</replaceable> [ <replaceable>frame_exclusion</replaceable> ] [row_pattern_common_syntax] +{ RANGE | ROWS | GROUPS } BETWEEN <replaceable>frame_start</replaceable> AND <replaceable>frame_end</replaceable> [ <replaceable>frame_exclusion</replaceable> ] [row_pattern_common_syntax] </synopsis> where <replaceable>frame_start</replaceable> @@ -1077,6 +1077,40 @@ EXCLUDE NO OTHERS a given peer group will be in the frame or excluded from it. </para> + <para> + The + optional <replaceable class="parameter">row_pattern_common_syntax</replaceable> + defines the <firstterm>row pattern recognition condition</firstterm> for + this + window. <replaceable class="parameter">row_pattern_common_syntax</replaceable> + includes following subclauses. <literal>AFTER MATCH SKIP PAST LAST + ROW</literal> or <literal>AFTER MATCH SKIP TO NEXT ROW</literal> controls + how to proceed to next row position after a match + found. With <literal>AFTER MATCH SKIP PAST LAST ROW</literal> (the + default) next row position is next to the last row of previous match. On + the other hand, with <literal>AFTER MATCH SKIP TO NEXT ROW</literal> next + row position is always next to the last row of previous + match. <literal>DEFINE</literal> defines definition variables along with a + boolean expression. <literal>PATTERN</literal> defines a sequence of rows + that satisfies certain conditions using variables defined + in <literal>DEFINE</literal> clause. If the variable is not defined in + the <literal>DEFINE</literal> clause, it is implicitly assumed + following is defined in the <literal>DEFINE</literal> clause. + +<synopsis> +<literal>variable_name</literal> AS TRUE +</synopsis> + + Note that the maximu number of variables defined + in <literal>DEFINE</literal> clause is 26. + +<synopsis> +[ AFTER MATCH SKIP PAST LAST ROW | AFTER MATCH SKIP TO NEXT ROW ] +PATTERN <replaceable class="parameter">pattern_variable_name</replaceable>[+] [, ...] +DEFINE <replaceable class="parameter">definition_varible_name</replaceable> AS <replaceable class="parameter">expression</replaceable> [, ...] +</synopsis> + </para> + <para> The purpose of a <literal>WINDOW</literal> clause is to specify the behavior of <firstterm>window functions</firstterm> appearing in the query's -- 2.25.1 ----Next_Part(Mon_Aug_26_13_39_47_2024_878)-- Content-Type: Text/X-Patch; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="v21-0007-Row-pattern-recognition-patch-tests.patch" ^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: postgres_fdw: Provide better emulation of READ COMMITTED behavior @ 2024-12-05 17:37 Robert Haas <[email protected]> 0 siblings, 2 replies; 4+ messages in thread From: Robert Haas @ 2024-12-05 17:37 UTC (permalink / raw) To: Etsuro Fujita <[email protected]>; +Cc: pgsql-hackers On Thu, Dec 5, 2024 at 4:41 AM Etsuro Fujita <[email protected]> wrote: > Comments welcome! Maybe I am missing something, though. I have a hard time seeing how this would work if cursors are in use on the main server. Say I do this: DECLARE foo CURSOR FOR SELECT * FROM ft1 UNION ALL SELECT * FROM ft2; ...fetch some rows from cursor foo but few enough that we only scan ft1... ...do something that causes a snapshot refresh like issue another query... ...fetch more rows from cursor foo until we start scanning ft2... -- Robert Haas EDB: http://www.enterprisedb.com ^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: postgres_fdw: Provide better emulation of READ COMMITTED behavior @ 2024-12-06 10:50 Andy Fan <[email protected]> parent: Robert Haas <[email protected]> 1 sibling, 0 replies; 4+ messages in thread From: Andy Fan @ 2024-12-06 10:50 UTC (permalink / raw) To: Robert Haas <[email protected]>; +Cc: Etsuro Fujita <[email protected]>; pgsql-hackers Robert Haas <[email protected]> writes: > On Thu, Dec 5, 2024 at 4:41 AM Etsuro Fujita <[email protected]> wrote: >> Comments welcome! Maybe I am missing something, though. > > I have a hard time seeing how this would work if cursors are in use on > the main server. Say I do this: > > DECLARE foo CURSOR FOR SELECT * FROM ft1 UNION ALL SELECT * FROM ft2; > ...fetch some rows from cursor foo but few enough that we only scan ft1... > ...do something that causes a snapshot refresh like issue another query... > ...fetch more rows from cursor foo until we start scanning ft2... Apart from the above issue, what do you think about that we are using a 'SELECT pg_catalog.pg_refresh_snapshot()' to let the remote do the refresh_snapshot VS 'a new message type for this'? There are lots of things happen in the 'SELECT' way like 'a extra network communication', 'a complete parser-planner-executor workflow.' With a new message type for this, we can send the message character with the next query together. if so, can the two overheads removed? -- Best Regards Andy Fan ^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: postgres_fdw: Provide better emulation of READ COMMITTED behavior @ 2024-12-07 09:02 Etsuro Fujita <[email protected]> parent: Robert Haas <[email protected]> 1 sibling, 0 replies; 4+ messages in thread From: Etsuro Fujita @ 2024-12-07 09:02 UTC (permalink / raw) To: Robert Haas <[email protected]>; +Cc: pgsql-hackers On Fri, Dec 6, 2024 at 2:37 AM Robert Haas <[email protected]> wrote: > I have a hard time seeing how this would work if cursors are in use on > the main server. Say I do this: > > DECLARE foo CURSOR FOR SELECT * FROM ft1 UNION ALL SELECT * FROM ft2; > ...fetch some rows from cursor foo but few enough that we only scan ft1... > ...do something that causes a snapshot refresh like issue another query... > ...fetch more rows from cursor foo until we start scanning ft2... Good point! Maybe my explanation was not enough, but the proposed patch does not allow any query to do a snapshot refresh if such open cursors exist on the main server, so cursor foo is guaranteed to scan ft2 using the same snapshot that was used to scan ft1. Thank you for taking the time for this proposal! Best regards, Etsuro Fujita ^ permalink raw reply [nested|flat] 4+ messages in thread
end of thread, other threads:[~2024-12-07 09:02 UTC | newest] Thread overview: 4+ messages (download: mbox mbox.gz follow: Atom feed) -- links below jump to the message on this page -- 2024-08-26 04:32 [PATCH v21 6/8] Row pattern recognition patch (docs). Tatsuo Ishii <[email protected]> 2024-12-05 17:37 Re: postgres_fdw: Provide better emulation of READ COMMITTED behavior Robert Haas <[email protected]> 2024-12-06 10:50 ` Re: postgres_fdw: Provide better emulation of READ COMMITTED behavior Andy Fan <[email protected]> 2024-12-07 09:02 ` Re: postgres_fdw: Provide better emulation of READ COMMITTED behavior Etsuro Fujita <[email protected]>
This inbox is served by agora; see mirroring instructions for how to clone and mirror all data and code used for this inbox