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help / color / mirror / Atom feedFrom: Zhang Mingli <[email protected]>
To: Sami Imseih <[email protected]>
To: Michael Paquier <[email protected]>
Cc: Álvaro Herrera <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Subject: Re: Proposal to CREATE FOREIGN TABLE LIKE
Date: Mon, 17 Feb 2025 19:14:59 +0800
Message-ID: <ae691413-72c5-4f17-8a31-141f70bbabd6@Spark> (raw)
In-Reply-To: <[email protected]>
References: <CANG7CA+W=KeYFGqGEtoaZy7iV6VHWnrhbBnWrbNt_vgmAuw3Rg@mail.gmail.com>
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On Feb 17, 2025 at 15:24 +0800, Michael Paquier <[email protected]>, wrote:
>
> + * For foreign tables, they have no storage in Postgres.
> + * Inapplicable options are ignored.
>
> Wording is a bit strange here.
Hi, is this better?
* Foreign tables do not store data in Postgres.
* Any options that are not applicable for foreign tables will be ignored:
> + * CREATE_TABLE_LIKE_COMPRESSION
> + * CREATE_TABLE_LIKE_IDENTITY
> + * CREATE_TABLE_LIKE_STORAGE
> + * CREATE_TABLE_LIKE_INDEXES
> [...]
> +DROP FOREIGN TABLE ctl_foreign_table1;
> +DROP FOREIGN TABLE ctl_foreign_table2;
> +DROP FOREIGN TABLE ctl_foreign_table3;
> +DROP FOREIGN TABLE ctl_foreign_table4;
> +DROP FOREIGN TABLE ctl_foreign_table5;
> +DROP FOREIGN TABLE ctl_foreign_table6;
>
> What's the point of creating that many tables, one for each of the
> four INCLUDING options you are testing? It is possible to stack all
> of them in a single CREATE TABLE command, still is that really
> necessary if we have coverage with INCLUDING ALL and EXCLUDING ALL
> (perhaps write it directly in the CREATE query rather than assume that
> it is the default) as these are all-or-nothing switches for all the
> option values. Of course let's be careful with HIDE_TOAST_COMPRESSION
> if need be.
I usually follow the cases within the same file; for each independent option, it becomes easier to identify which options are valid or invalid.
However, if you believe consolidating them into one is better, I’m fine with that. Updated.
> Perhaps the original table should have a primary key, also to track
> the fact that the NOT NULL constraint is always copied but its related
> index is not? Identity columns assign a NOT NULL constraint, as
> documented these are always copied. Just wanted to point out that
> this works the same way for your implementation with foreign tables,
> so perhaps we should have a test for that.
Done, although there is already one in column d.
>
> Glad to see that you did not forget about statistics. I didn't recall
> that these were OK for foreign tables, TBH.
I also didn't realize this until I wrote this patch. This could be useful for the planner？
> expandTableLikeClause() depends on the "constr" built in the first
> phase of transformTableLikeClause() to bypass the parts related to
> generated, default and constraints properties. This dependency
> between both routines should be documented, I guess. Hmm.. Not sure
> where.
Comments are addressed except for this one, it might be worth considering another patch.
--
Zhang Mingli
HashData
Attachments:
[application/octet-stream] v5-0001-CREATE-FOREIGN-TABLE-LIKE.patch (16.5K, ../ae691413-72c5-4f17-8a31-141f70bbabd6@Spark/3-v5-0001-CREATE-FOREIGN-TABLE-LIKE.patch)
download | inline diff:
From ef05c075ff6390712d6c32c455d9fe50c0004b54 Mon Sep 17 00:00:00 2001
From: Zhang Mingli <[email protected]>
Date: Tue, 11 Feb 2025 22:38:49 +0800
Subject: [PATCH] CREATE FOREIGN TABLE LIKE
Added support for CREATE FOREIGN TABLE LIKE to enable the creation of
foreign tables based on the column definitions, constraints of existing
source tables.
This feature mirrors the behavior of CREATE TABLE LIKE,
but ignores inapplicable options such as INCLUDING INDEXES,
INCLUDING COMPRESSION, INCLUDING IDENTITY, INCLUDING STORAGE
for foreign tables.
Authored-by: Zhang Mingli [email protected]
---
doc/src/sgml/ref/create_foreign_table.sgml | 118 +++++++++++++++++-
src/backend/parser/parse_utilcmd.c | 28 +++--
.../regress/expected/create_table_like.out | 77 ++++++++++++
src/test/regress/sql/create_table_like.sql | 34 +++++
4 files changed, 245 insertions(+), 12 deletions(-)
diff --git a/doc/src/sgml/ref/create_foreign_table.sgml b/doc/src/sgml/ref/create_foreign_table.sgml
index 0dcd9ca6f8..5bc0a11009 100644
--- a/doc/src/sgml/ref/create_foreign_table.sgml
+++ b/doc/src/sgml/ref/create_foreign_table.sgml
@@ -23,7 +23,8 @@ PostgreSQL documentation
<synopsis>
CREATE FOREIGN TABLE [ IF NOT EXISTS ] <replaceable class="parameter">table_name</replaceable> ( [
{ <replaceable class="parameter">column_name</replaceable> <replaceable class="parameter">data_type</replaceable> [ OPTIONS ( <replaceable class="parameter">option</replaceable> '<replaceable class="parameter">value</replaceable>' [, ... ] ) ] [ COLLATE <replaceable>collation</replaceable> ] [ <replaceable class="parameter">column_constraint</replaceable> [ ... ] ]
- | <replaceable>table_constraint</replaceable> }
+ | <replaceable>table_constraint</replaceable>
+ | LIKE <replaceable>source_table</replaceable> [ <replaceable>like_option</replaceable> ... ] }
[, ... ]
] )
[ INHERITS ( <replaceable>parent_table</replaceable> [, ... ] ) ]
@@ -57,6 +58,10 @@ CREATE FOREIGN TABLE [ IF NOT EXISTS ] <replaceable class="parameter">table_name
CHECK ( <replaceable class="parameter">expression</replaceable> ) [ NO INHERIT ] }
[ ENFORCED | NOT ENFORCED ]
+<phrase>and <replaceable class="parameter">like_option</replaceable> is:</phrase>
+
+{ INCLUDING | EXCLUDING } { COMMENTS | CONSTRAINTS | DEFAULTS | GENERATED | STATISTICS | ALL }
+
<phrase>and <replaceable class="parameter">partition_bound_spec</replaceable> is:</phrase>
IN ( <replaceable class="parameter">partition_bound_expr</replaceable> [, ...] ) |
@@ -191,6 +196,117 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
</listitem>
</varlistentry>
+ <varlistentry>
+ <term><literal>LIKE <replaceable>source_table</replaceable> [ <replaceable>like_option</replaceable> ... ]</literal></term>
+ <listitem>
+ <para>
+ The <literal>LIKE</literal> clause specifies a table from which
+ the new table automatically copies all column names, their data types,
+ and their not-null constraints.
+ </para>
+ <para>
+ Unlike <literal>INHERITS</literal>, the new table and original table
+ are completely decoupled after creation is complete. Changes to the
+ original table will not be applied to the new table, and it is not
+ possible to include data of the new table in scans of the original
+ table.
+ </para>
+ <para>
+ Also unlike <literal>INHERITS</literal>, columns and
+ constraints copied by <literal>LIKE</literal> are not merged with similarly
+ named columns and constraints.
+ If the same name is specified explicitly or in another
+ <literal>LIKE</literal> clause, an error is signaled.
+ </para>
+ <para>
+ The optional <replaceable>like_option</replaceable> clauses specify
+ which additional properties of the original table to copy. Specifying
+ <literal>INCLUDING</literal> copies the property, specifying
+ <literal>EXCLUDING</literal> omits the property.
+ <literal>EXCLUDING</literal> is the default. If multiple specifications
+ are made for the same kind of object, the last one is used. The
+ available options are:
+
+ <variablelist>
+ <varlistentry>
+ <term><literal>INCLUDING COMMENTS</literal></term>
+ <listitem>
+ <para>
+ Comments for the copied columns, constraints, and indexes will be
+ copied. The default behavior is to exclude comments, resulting in
+ the copied columns and constraints in the new table having no
+ comments.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><literal>INCLUDING CONSTRAINTS</literal></term>
+ <listitem>
+ <para>
+ <literal>CHECK</literal> constraints will be copied. No distinction
+ is made between column constraints and table constraints. Not-null
+ constraints are always copied to the new table.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><literal>INCLUDING DEFAULTS</literal></term>
+ <listitem>
+ <para>
+ Default expressions for the copied column definitions will be
+ copied. Otherwise, default expressions are not copied, resulting in
+ the copied columns in the new table having null defaults. Note that
+ copying defaults that call database-modification functions, such as
+ <function>nextval</function>, may create a functional linkage
+ between the original and new tables.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><literal>INCLUDING GENERATED</literal></term>
+ <listitem>
+ <para>
+ Any generation expressions of copied column definitions will be
+ copied. By default, new columns will be regular base columns.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><literal>INCLUDING STATISTICS</literal></term>
+ <listitem>
+ <para>
+ Extended statistics are copied to the new table.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><literal>INCLUDING ALL</literal></term>
+ <listitem>
+ <para>
+ <literal>INCLUDING ALL</literal> is an abbreviated form selecting
+ all the available individual options. (It could be useful to write
+ individual <literal>EXCLUDING</literal> clauses after
+ <literal>INCLUDING ALL</literal> to select all but some specific
+ options.)
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </para>
+
+ <para>
+ Foreign tables have no storage in PostgreSQL.
+ Inapplicable options: <literal>INCLUDING INDEXES</literal>, <literal>INCLUDING STORAGE</literal>,
+ <literal>INCLUDING COMPRESSION</literal>, <literal>INCLUDING IDENTITY</literal> are ignored.
+ </para>
+ </listitem>
+ </varlistentry>
+
<varlistentry>
<term><literal>CONSTRAINT <replaceable class="parameter">constraint_name</replaceable></literal></term>
<listitem>
diff --git a/src/backend/parser/parse_utilcmd.c b/src/backend/parser/parse_utilcmd.c
index ca028d2a66..443bf2534f 100644
--- a/src/backend/parser/parse_utilcmd.c
+++ b/src/backend/parser/parse_utilcmd.c
@@ -1117,6 +1117,14 @@ transformTableConstraint(CreateStmtContext *cxt, Constraint *constraint)
* process at this point, add the TableLikeClause to cxt->likeclauses, which
* will cause utility.c to call expandTableLikeClause() after the new
* table has been created.
+ *
+ * Foreign tables do not store data in Postgres.
+ * Any options that are not applicable for foreign tables will be ignored:
+ * CREATE_TABLE_LIKE_COMPRESSION
+ * CREATE_TABLE_LIKE_IDENTITY
+ * CREATE_TABLE_LIKE_STORAGE
+ * CREATE_TABLE_LIKE_INDEXES
+ * while INDEXES is handled in expandTableLikeClause() later.
*/
static void
transformTableLikeClause(CreateStmtContext *cxt, TableLikeClause *table_like_clause)
@@ -1131,12 +1139,6 @@ transformTableLikeClause(CreateStmtContext *cxt, TableLikeClause *table_like_cla
setup_parser_errposition_callback(&pcbstate, cxt->pstate,
table_like_clause->relation->location);
- /* we could support LIKE in many cases, but worry about it another day */
- if (cxt->isforeign)
- ereport(ERROR,
- (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
- errmsg("LIKE is not supported for creating foreign tables")));
-
/* Open the relation referenced by the LIKE clause */
relation = relation_openrv(table_like_clause->relation, AccessShareLock);
@@ -1217,7 +1219,8 @@ transformTableLikeClause(CreateStmtContext *cxt, TableLikeClause *table_like_cla
* Copy identity if requested
*/
if (attribute->attidentity &&
- (table_like_clause->options & CREATE_TABLE_LIKE_IDENTITY))
+ (table_like_clause->options & CREATE_TABLE_LIKE_IDENTITY) &&
+ !cxt->isforeign)
{
Oid seq_relid;
List *seq_options;
@@ -1236,14 +1239,16 @@ transformTableLikeClause(CreateStmtContext *cxt, TableLikeClause *table_like_cla
}
/* Likewise, copy storage if requested */
- if (table_like_clause->options & CREATE_TABLE_LIKE_STORAGE)
+ if ((table_like_clause->options & CREATE_TABLE_LIKE_STORAGE) &&
+ !cxt->isforeign)
def->storage = attribute->attstorage;
else
def->storage = 0;
/* Likewise, copy compression if requested */
- if ((table_like_clause->options & CREATE_TABLE_LIKE_COMPRESSION) != 0
- && CompressionMethodIsValid(attribute->attcompression))
+ if ((table_like_clause->options & CREATE_TABLE_LIKE_COMPRESSION) != 0 &&
+ CompressionMethodIsValid(attribute->attcompression) &&
+ !cxt->isforeign)
def->compression =
pstrdup(GetCompressionMethodName(attribute->attcompression));
else
@@ -1522,7 +1527,8 @@ expandTableLikeClause(RangeVar *heapRel, TableLikeClause *table_like_clause)
* Process indexes if required.
*/
if ((table_like_clause->options & CREATE_TABLE_LIKE_INDEXES) &&
- relation->rd_rel->relhasindex)
+ relation->rd_rel->relhasindex &&
+ childrel->rd_rel->relkind != RELKIND_FOREIGN_TABLE)
{
List *parent_indexes;
ListCell *l;
diff --git a/src/test/regress/expected/create_table_like.out b/src/test/regress/expected/create_table_like.out
index e061389135..c38118a8ad 100644
--- a/src/test/regress/expected/create_table_like.out
+++ b/src/test/regress/expected/create_table_like.out
@@ -563,3 +563,80 @@ DROP TYPE ctlty1;
DROP VIEW ctlv1;
DROP TABLE IF EXISTS ctlt4, ctlt10, ctlt11, ctlt11a, ctlt12;
NOTICE: table "ctlt10" does not exist, skipping
+--
+-- CREATE FOREIGN TABLE LIKE
+--
+CREATE FOREIGN DATA WRAPPER ctl_dummy;
+CREATE SERVER ctl_s0 FOREIGN DATA WRAPPER ctl_dummy;
+CREATE TABLE ctl_table(a int primary key, b varchar COMPRESSION pglz,
+ c int GENERATED ALWAYS AS (a * 2) STORED,
+ d bigint GENERATED ALWAYS AS IDENTITY,
+ e int default 1);
+CREATE INDEX ctl_table_a_key ON ctl_table(a);
+COMMENT ON COLUMN ctl_table.b IS 'Column b';
+CREATE STATISTICS ctl_table_stat ON a,b FROM ctl_table;
+ALTER TABLE ctl_table add constraint foo CHECK (b = 'text');
+\d+ ctl_table
+ Table "public.ctl_table"
+ Column | Type | Collation | Nullable | Default | Storage | Stats target | Description
+--------+-------------------+-----------+----------+------------------------------------+----------+--------------+-------------
+ a | integer | | not null | | plain | |
+ b | character varying | | | | extended | | Column b
+ c | integer | | | generated always as (a * 2) stored | plain | |
+ d | bigint | | not null | generated always as identity | plain | |
+ e | integer | | | 1 | plain | |
+Indexes:
+ "ctl_table_pkey" PRIMARY KEY, btree (a)
+ "ctl_table_a_key" btree (a)
+Check constraints:
+ "foo" CHECK (b::text = 'text'::text)
+Statistics objects:
+ "public.ctl_table_stat" ON a, b FROM ctl_table
+Not-null constraints:
+ "ctl_table_a_not_null" NOT NULL "a"
+ "ctl_table_d_not_null" NOT NULL "d"
+
+-- Test EXCLUDING ALL
+CREATE FOREIGN TABLE ctl_foreign_table1(LIKE ctl_table EXCLUDING ALL) SERVER ctl_s0;
+\d+ ctl_foreign_table1
+ Foreign table "public.ctl_foreign_table1"
+ Column | Type | Collation | Nullable | Default | FDW options | Storage | Stats target | Description
+--------+-------------------+-----------+----------+---------+-------------+----------+--------------+-------------
+ a | integer | | not null | | | plain | |
+ b | character varying | | | | | extended | |
+ c | integer | | | | | plain | |
+ d | bigint | | not null | | | plain | |
+ e | integer | | | | | plain | |
+Not-null constraints:
+ "ctl_table_a_not_null" NOT NULL "a"
+ "ctl_table_d_not_null" NOT NULL "d"
+Server: ctl_s0
+
+\set HIDE_TOAST_COMPRESSION false
+-- Test INCLUDING ALL
+-- INDEXES, IDENTITY, COMPRESSION, STORAGE are not copied.
+CREATE FOREIGN TABLE ctl_foreign_table2(LIKE ctl_table INCLUDING ALL) SERVER ctl_s0;
+\d+ ctl_foreign_table2
+ Foreign table "public.ctl_foreign_table2"
+ Column | Type | Collation | Nullable | Default | FDW options | Storage | Stats target | Description
+--------+-------------------+-----------+----------+------------------------------------+-------------+----------+--------------+-------------
+ a | integer | | not null | | | plain | |
+ b | character varying | | | | | extended | | Column b
+ c | integer | | | generated always as (a * 2) stored | | plain | |
+ d | bigint | | not null | | | plain | |
+ e | integer | | | 1 | | plain | |
+Check constraints:
+ "foo" CHECK (b::text = 'text'::text)
+Statistics objects:
+ "public.ctl_foreign_table2_a_b_stat" ON a, b FROM ctl_foreign_table2
+Not-null constraints:
+ "ctl_table_a_not_null" NOT NULL "a"
+ "ctl_table_d_not_null" NOT NULL "d"
+Server: ctl_s0
+
+\set HIDE_TOAST_COMPRESSION true
+DROP TABLE ctl_table;
+DROP FOREIGN TABLE ctl_foreign_table1;
+DROP FOREIGN TABLE ctl_foreign_table2;
+DROP FOREIGN DATA WRAPPER ctl_dummy CASCADE;
+NOTICE: drop cascades to server ctl_s0
diff --git a/src/test/regress/sql/create_table_like.sql b/src/test/regress/sql/create_table_like.sql
index a41f8b83d7..98ca8ac060 100644
--- a/src/test/regress/sql/create_table_like.sql
+++ b/src/test/regress/sql/create_table_like.sql
@@ -225,3 +225,37 @@ DROP SEQUENCE ctlseq1;
DROP TYPE ctlty1;
DROP VIEW ctlv1;
DROP TABLE IF EXISTS ctlt4, ctlt10, ctlt11, ctlt11a, ctlt12;
+
+--
+-- CREATE FOREIGN TABLE LIKE
+--
+CREATE FOREIGN DATA WRAPPER ctl_dummy;
+CREATE SERVER ctl_s0 FOREIGN DATA WRAPPER ctl_dummy;
+
+CREATE TABLE ctl_table(a int primary key, b varchar COMPRESSION pglz,
+ c int GENERATED ALWAYS AS (a * 2) STORED,
+ d bigint GENERATED ALWAYS AS IDENTITY,
+ e int default 1);
+
+CREATE INDEX ctl_table_a_key ON ctl_table(a);
+COMMENT ON COLUMN ctl_table.b IS 'Column b';
+CREATE STATISTICS ctl_table_stat ON a,b FROM ctl_table;
+ALTER TABLE ctl_table add constraint foo CHECK (b = 'text');
+
+\d+ ctl_table
+
+-- Test EXCLUDING ALL
+CREATE FOREIGN TABLE ctl_foreign_table1(LIKE ctl_table EXCLUDING ALL) SERVER ctl_s0;
+\d+ ctl_foreign_table1
+
+\set HIDE_TOAST_COMPRESSION false
+-- Test INCLUDING ALL
+-- INDEXES, IDENTITY, COMPRESSION, STORAGE are not copied.
+CREATE FOREIGN TABLE ctl_foreign_table2(LIKE ctl_table INCLUDING ALL) SERVER ctl_s0;
+\d+ ctl_foreign_table2
+\set HIDE_TOAST_COMPRESSION true
+
+DROP TABLE ctl_table;
+DROP FOREIGN TABLE ctl_foreign_table1;
+DROP FOREIGN TABLE ctl_foreign_table2;
+DROP FOREIGN DATA WRAPPER ctl_dummy CASCADE;
--
2.34.1
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Subject: Re: Proposal to CREATE FOREIGN TABLE LIKE
In-Reply-To: <ae691413-72c5-4f17-8a31-141f70bbabd6@Spark>
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