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Generated columns

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This is an SQL-standard feature that allows creating columns that are
computed from expressions rather than assigned, similar to a view or
materialized view but on a column basis.

This implements one kind of generated column: stored (computed on
write).  Another kind, virtual (computed on read), is planned for the
future, and some room is left for it.

Reviewed-by: Michael Paquier <michael@paquier.xyz>
Reviewed-by: Pavel Stehule <pavel.stehule@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/b151f851-4019-bdb1-699e-ebab07d2f40a@2ndquadrant.com
This commit is contained in:
Peter Eisentraut
2019-03-30 08:13:09 +01:00
parent 6b8b5364dd
commit fc22b6623b
84 changed files with 3067 additions and 157 deletions
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45
doc/src/sgml/ref/create_table.sgml
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@@ -62,6 +62,7 @@ CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXI
NULL |
CHECK ( <replaceable class="parameter">expression</replaceable> ) [ NO INHERIT ] |
DEFAULT <replaceable>default_expr</replaceable> |
GENERATED ALWAYS AS ( <replaceable>generation_expr</replaceable> ) STORED |
GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( <replaceable>sequence_options</replaceable> ) ] |
UNIQUE <replaceable class="parameter">index_parameters</replaceable> |
PRIMARY KEY <replaceable class="parameter">index_parameters</replaceable> |
@@ -83,7 +84,7 @@ class="parameter">referential_action</replaceable> ] [ ON UPDATE <replaceable cl
<phrase>and <replaceable class="parameter">like_option</replaceable> is:</phrase>
{ INCLUDING | EXCLUDING } { COMMENTS | CONSTRAINTS | DEFAULTS | IDENTITY | INDEXES | STATISTICS | STORAGE | ALL }
{ INCLUDING | EXCLUDING } { COMMENTS | CONSTRAINTS | DEFAULTS | GENERATED | IDENTITY | INDEXES | STATISTICS | STORAGE | ALL }
<phrase>and <replaceable class="parameter">partition_bound_spec</replaceable> is:</phrase>
@@ -627,6 +628,16 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
</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 IDENTITY</literal></term>
<listitem>
@@ -797,6 +808,28 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
</listitem>
</varlistentry>
<varlistentry>
<term><literal>GENERATED ALWAYS AS ( <replaceable>generation_expr</replaceable> ) STORED</literal><indexterm><primary>generated column</primary></indexterm></term>
<listitem>
<para>
This clause creates the column as a <firstterm>generated
column</firstterm>. The column cannot be written to, and when read it
will be computed from the specified expression.
</para>
<para>
The keyword <literal>STORED</literal> is required to signify that the
column will be computed on write and will be stored on disk. default.
</para>
<para>
The generation expression can refer to other columns in the table, but
not other generated columns. Any functions and operators used must be
immutable. References to other tables are not allowed.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( <replaceable>sequence_options</replaceable> ) ]</literal></term>
<listitem>
@@ -2028,6 +2061,16 @@ CREATE TABLE cities_partdef
</para>
</refsect2>
<refsect2>
<title>Generated Columns</title>
<para>
The option <literal>STORED</literal> is not standard but is also used by
other SQL implementations. The SQL standard does not specify the storage
of generated columns.
</para>
</refsect2>
<refsect2>
<title><literal>LIKE</literal> Clause</title>