Add table_constraint synopsis to ALTER TABLE documentation.

This is already present in the CREATE TABLE documentation, but it's
nicer not to have to refer to CREATE TABLE to find out the syntax
for ALTER TABLE.

Lætitia Avrot

doc/src/sgml/ref/alter_table.sgml

@@ -85,6 +85,17 @@ ALTER TABLE [ IF EXISTS ] <replaceable class="parameter">name</replaceable>
     OWNER TO { <replaceable class="parameter">new_owner</replaceable> | CURRENT_USER | SESSION_USER }
     REPLICA IDENTITY { DEFAULT | USING INDEX <replaceable class="parameter">index_name</replaceable> | FULL | NOTHING }
 
+<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 ] |
+  UNIQUE ( <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> [, ... ] ) ]
+    [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ] [ ON DELETE <replaceable class="parameter">action</replaceable> ] [ ON UPDATE <replaceable class="parameter">action</replaceable> ] }
+[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
+
 <phrase>and <replaceable class="parameter">table_constraint_using_index</replaceable> is:</phrase>
 
     [ CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> ]