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4th chunk of `doc/src/sgml/ref/alter_table.sgml`
0ff6b71c922c9ef813e28b86a16dfc79130047a38969c7470000000100000faa
 INITIALLY IMMEDIATE ] [ ENFORCED | NOT ENFORCED ]

<phrase>and <replaceable class="parameter">table_constraint</replaceable> is:</phrase>

[ CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> ]
{ CHECK ( <replaceable class="parameter">expression</replaceable> ) [ NO INHERIT ] |
  NOT NULL <replaceable class="parameter">column_name</replaceable> [ NO INHERIT ] |
  UNIQUE [ NULLS [ NOT ] DISTINCT ] ( <replaceable class="parameter">column_name</replaceable> [, ... ] [, <replaceable class="parameter">column_name</replaceable> WITHOUT OVERLAPS ] ) <replaceable class="parameter">index_parameters</replaceable> |
  PRIMARY KEY ( <replaceable class="parameter">column_name</replaceable> [, ... ] [, <replaceable class="parameter">column_name</replaceable> WITHOUT OVERLAPS ] ) <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> [, ... ] [, PERIOD <replaceable class="parameter">column_name</replaceable> ] ) REFERENCES <replaceable class="parameter">reftable</replaceable> [ ( <replaceable class="parameter">refcolumn</replaceable> [, ... ]  [, PERIOD <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> ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ] [ ENFORCED | NOT ENFORCED ]

<phrase>and <replaceable class="parameter">table_constraint_using_index</replaceable> is:</phrase>

    [ CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> ]
    { UNIQUE | PRIMARY KEY } USING INDEX <replaceable class="parameter">index_name</replaceable>
    [ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]

<phrase><replaceable class="parameter">index_parameters</replaceable> in <literal>UNIQUE</literal>, <literal>PRIMARY KEY</literal>, and <literal>EXCLUDE</literal> constraints are:</phrase>

[ INCLUDE ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) ]
[ WITH ( <replaceable class="parameter">storage_parameter</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) ]
[ USING INDEX TABLESPACE <replaceable class="parameter">tablespace_name</replaceable> ]

<phrase><replaceable class="parameter">exclude_element</replaceable> in an <literal>EXCLUDE</literal> constraint is:</phrase>

{ <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 } ]

<phrase><replaceable class="parameter">referential_action</replaceable> in a <literal>FOREIGN KEY</literal>/<literal>REFERENCES</literal> constraint is:</phrase>

{ NO ACTION | RESTRICT | CASCADE | SET NULL [ ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) ] | SET DEFAULT [ ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) ] }
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <command>ALTER TABLE</command> changes the definition of an existing table.
   There are several subforms described below. Note that the lock level required
   may differ for each subform. An <literal>ACCESS EXCLUSIVE</literal> lock is
   acquired unless explicitly
Title: ALTER TABLE Syntax Details: Constraints and Actions
Summary
This section elaborates on the syntax for ALTER TABLE, focusing on table constraints, including CHECK, NOT NULL, UNIQUE, PRIMARY KEY, EXCLUDE, and FOREIGN KEY constraints. It details options like index parameters, exclusion elements, referential actions (NO ACTION, RESTRICT, CASCADE, SET NULL, SET DEFAULT), and how to specify index methods and predicates within constraints. It also explains the use of DEFERRABLE, INITIALLY DEFERRED/IMMEDIATE, and ENFORCED/NOT ENFORCED constraint options.