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-rw-r--r--doc/src/sgml/catalogs.sgml13
-rw-r--r--doc/src/sgml/ddl.sgml29
-rw-r--r--doc/src/sgml/information_schema.sgml12
-rw-r--r--doc/src/sgml/ref/alter_table.sgml4
-rw-r--r--doc/src/sgml/ref/create_index.sgml13
-rw-r--r--doc/src/sgml/ref/create_table.sgml11
6 files changed, 70 insertions, 12 deletions
diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index 7d5b0b1656c..879d2dbce03 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -4267,6 +4267,19 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&l
<row>
<entry role="catalog_table_entry"><para role="column_definition">
+ <structfield>indnullsnotdistinct</structfield> <type>bool</type>
+ </para>
+ <para>
+ This value is only used for unique indexes. If false, this unique
+ index will consider null values distinct (so the index can contain
+ multiple null values in a column, the default PostgreSQL behavior). If
+ it is true, it will consider null values to be equal (so the index can
+ only contain one null value in a column).
+ </para></entry>
+ </row>
+
+ <row>
+ <entry role="catalog_table_entry"><para role="column_definition">
<structfield>indisprimary</structfield> <type>bool</type>
</para>
<para>
diff --git a/doc/src/sgml/ddl.sgml b/doc/src/sgml/ddl.sgml
index 7cf0f0da3b2..296f3ff59df 100644
--- a/doc/src/sgml/ddl.sgml
+++ b/doc/src/sgml/ddl.sgml
@@ -759,14 +759,33 @@ CREATE TABLE products (
In general, a unique constraint is violated if there is more than
one row in the table where the values of all of the
columns included in the constraint are equal.
- However, two null values are never considered equal in this
+ By default, two null values are not considered equal in this
comparison. That means even in the presence of a
unique constraint it is possible to store duplicate
rows that contain a null value in at least one of the constrained
- columns. This behavior conforms to the SQL standard, but we have
- heard that other SQL databases might not follow this rule. So be
- careful when developing applications that are intended to be
- portable.
+ columns. This behavior can be changed by adding the clause <literal>NULLS
+ NOT DISTINCT</literal>, like
+<programlisting>
+CREATE TABLE products (
+ product_no integer UNIQUE <emphasis>NULLS NOT DISTINCT</emphasis>,
+ name text,
+ price numeric
+);
+</programlisting>
+ or
+<programlisting>
+CREATE TABLE products (
+ product_no integer,
+ name text,
+ price numeric,
+ UNIQUE <emphasis>NULLS NOT DISTINCT</emphasis> (product_no)
+);
+</programlisting>
+ The default behavior can be specified explicitly using <literal>NULLS
+ DISTINCT</literal>. The default null treatment in unique constraints is
+ implementation-defined according to the SQL standard, and other
+ implementations have a different behavior. So be careful when developing
+ applications that are intended to be portable.
</para>
</sect2>
diff --git a/doc/src/sgml/information_schema.sgml b/doc/src/sgml/information_schema.sgml
index c5e68c175f9..350c75bc31e 100644
--- a/doc/src/sgml/information_schema.sgml
+++ b/doc/src/sgml/information_schema.sgml
@@ -6899,6 +6899,18 @@ ORDER BY c.ordinal_position;
<literal>YES</literal>)
</para></entry>
</row>
+
+ <row>
+ <entry role="catalog_table_entry"><para role="column_definition">
+ <structfield>nulls_distinct</structfield> <type>yes_or_no</type>
+ </para>
+ <para>
+ If the constraint is a unique constraint, then <literal>YES</literal>
+ if the constraint treats nulls as distinct or <literal>NO</literal> if
+ it treats nulls as not distinct, otherwise null for other types of
+ constraints.
+ </para></entry>
+ </row>
</tbody>
</tgroup>
</table>
diff --git a/doc/src/sgml/ref/alter_table.sgml b/doc/src/sgml/ref/alter_table.sgml
index c8b16c115ed..dee026e3a08 100644
--- a/doc/src/sgml/ref/alter_table.sgml
+++ b/doc/src/sgml/ref/alter_table.sgml
@@ -103,7 +103,7 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
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> |
+ UNIQUE [ NULLS [ NOT ] DISTINCT ] <replaceable class="parameter">index_parameters</replaceable> |
PRIMARY KEY <replaceable class="parameter">index_parameters</replaceable> |
REFERENCES <replaceable class="parameter">reftable</replaceable> [ ( <replaceable class="parameter">refcolumn</replaceable> ) ] [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ]
[ ON DELETE <replaceable class="parameter">referential_action</replaceable> ] [ ON UPDATE <replaceable class="parameter">referential_action</replaceable> ] }
@@ -113,7 +113,7 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
[ CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> ]
{ CHECK ( <replaceable class="parameter">expression</replaceable> ) [ NO INHERIT ] |
- UNIQUE ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) <replaceable class="parameter">index_parameters</replaceable> |
+ UNIQUE [ NULLS [ NOT ] DISTINCT ] ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) <replaceable class="parameter">index_parameters</replaceable> |
PRIMARY KEY ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) <replaceable class="parameter">index_parameters</replaceable> |
EXCLUDE [ USING <replaceable class="parameter">index_method</replaceable> ] ( <replaceable class="parameter">exclude_element</replaceable> WITH <replaceable class="parameter">operator</replaceable> [, ... ] ) <replaceable class="parameter">index_parameters</replaceable> [ WHERE ( <replaceable class="parameter">predicate</replaceable> ) ] |
FOREIGN KEY ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) REFERENCES <replaceable class="parameter">reftable</replaceable> [ ( <replaceable class="parameter">refcolumn</replaceable> [, ... ] ) ]
diff --git a/doc/src/sgml/ref/create_index.sgml b/doc/src/sgml/ref/create_index.sgml
index 89a4d746f6f..91eaaabc90f 100644
--- a/doc/src/sgml/ref/create_index.sgml
+++ b/doc/src/sgml/ref/create_index.sgml
@@ -24,6 +24,7 @@ PostgreSQL documentation
CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] [ [ IF NOT EXISTS ] <replaceable class="parameter">name</replaceable> ] ON [ ONLY ] <replaceable class="parameter">table_name</replaceable> [ USING <replaceable class="parameter">method</replaceable> ]
( { <replaceable class="parameter">column_name</replaceable> | ( <replaceable class="parameter">expression</replaceable> ) } [ COLLATE <replaceable class="parameter">collation</replaceable> ] [ <replaceable class="parameter">opclass</replaceable> [ ( <replaceable class="parameter">opclass_parameter</replaceable> = <replaceable class="parameter">value</replaceable> [, ... ] ) ] ] [ ASC | DESC ] [ NULLS { FIRST | LAST } ] [, ...] )
[ INCLUDE ( <replaceable class="parameter">column_name</replaceable> [, ...] ) ]
+ [ NULLS [ NOT ] DISTINCT ]
[ WITH ( <replaceable class="parameter">storage_parameter</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) ]
[ TABLESPACE <replaceable class="parameter">tablespace_name</replaceable> ]
[ WHERE <replaceable class="parameter">predicate</replaceable> ]
@@ -335,6 +336,18 @@ CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] [ [ IF NOT EXISTS ] <replaceable class=
</varlistentry>
<varlistentry>
+ <term><literal>NULLS DISTINCT</literal></term>
+ <term><literal>NULLS NOT DISTINCT</literal></term>
+ <listitem>
+ <para>
+ Specifies whether for a unique index, null values should be considered
+ distinct (not equal). The default is that they are distinct, so that
+ a unique index could contain multiple null values in a column.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
<term><replaceable class="parameter">storage_parameter</replaceable></term>
<listitem>
<para>
diff --git a/doc/src/sgml/ref/create_table.sgml b/doc/src/sgml/ref/create_table.sgml
index b97bb9ded15..7e4ef312c0e 100644
--- a/doc/src/sgml/ref/create_table.sgml
+++ b/doc/src/sgml/ref/create_table.sgml
@@ -67,7 +67,7 @@ CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXI
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> |
+ UNIQUE [ NULLS [ NOT ] DISTINCT ] <replaceable class="parameter">index_parameters</replaceable> |
PRIMARY KEY <replaceable class="parameter">index_parameters</replaceable> |
REFERENCES <replaceable class="parameter">reftable</replaceable> [ ( <replaceable class="parameter">refcolumn</replaceable> ) ] [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ]
[ ON DELETE <replaceable class="parameter">referential_action</replaceable> ] [ ON UPDATE <replaceable class="parameter">referential_action</replaceable> ] }
@@ -77,7 +77,7 @@ CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXI
[ CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> ]
{ CHECK ( <replaceable class="parameter">expression</replaceable> ) [ NO INHERIT ] |
- UNIQUE ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) <replaceable class="parameter">index_parameters</replaceable> |
+ UNIQUE [ NULLS [ NOT ] DISTINCT ] ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) <replaceable class="parameter">index_parameters</replaceable> |
PRIMARY KEY ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) <replaceable class="parameter">index_parameters</replaceable> |
EXCLUDE [ USING <replaceable class="parameter">index_method</replaceable> ] ( <replaceable class="parameter">exclude_element</replaceable> WITH <replaceable class="parameter">operator</replaceable> [, ... ] ) <replaceable class="parameter">index_parameters</replaceable> [ WHERE ( <replaceable class="parameter">predicate</replaceable> ) ] |
FOREIGN KEY ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) REFERENCES <replaceable class="parameter">reftable</replaceable> [ ( <replaceable class="parameter">refcolumn</replaceable> [, ... ] ) ]
@@ -917,8 +917,8 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
</varlistentry>
<varlistentry>
- <term><literal>UNIQUE</literal> (column constraint)</term>
- <term><literal>UNIQUE ( <replaceable class="parameter">column_name</replaceable> [, ... ] )</literal>
+ <term><literal>UNIQUE [ NULLS [ NOT ] DISTINCT ]</literal> (column constraint)</term>
+ <term><literal>UNIQUE [ NULLS [ NOT ] DISTINCT ] ( <replaceable class="parameter">column_name</replaceable> [, ... ] )</literal>
<optional> <literal>INCLUDE ( <replaceable class="parameter">column_name</replaceable> [, ...])</literal> </optional> (table constraint)</term>
<listitem>
@@ -934,7 +934,8 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
<para>
For the purpose of a unique constraint, null values are not
- considered equal.
+ considered equal, unless <literal>NULLS NOT DISTINCT</literal> is
+ specified.
</para>
<para>
generated by cgit v1.2.3 (git 2.46.0) at 2025-08-13 13:39:23 +0000