diff options
Diffstat (limited to 'doc/src/sgml/ref/create_table.sgml')
| -rw-r--r-- | doc/src/sgml/ref/create_table.sgml | 40 |
1 files changed, 29 insertions, 11 deletions
diff --git a/doc/src/sgml/ref/create_table.sgml b/doc/src/sgml/ref/create_table.sgml index 64971752eb4..1f986bcd88c 100644 --- a/doc/src/sgml/ref/create_table.sgml +++ b/doc/src/sgml/ref/create_table.sgml @@ -1,5 +1,5 @@ <!-- -$PostgreSQL: pgsql/doc/src/sgml/ref/create_table.sgml,v 1.114 2009/02/12 13:25:33 momjian Exp $ +$PostgreSQL: pgsql/doc/src/sgml/ref/create_table.sgml,v 1.115 2009/07/29 20:56:17 tgl Exp $ PostgreSQL documentation --> @@ -35,8 +35,8 @@ CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } ] TABLE <replaceable class="PAR where <replaceable class="PARAMETER">column_constraint</replaceable> is: [ CONSTRAINT <replaceable class="PARAMETER">constraint_name</replaceable> ] -{ NOT NULL | - NULL | +{ NOT NULL | + NULL | UNIQUE <replaceable class="PARAMETER">index_parameters</replaceable> | PRIMARY KEY <replaceable class="PARAMETER">index_parameters</replaceable> | CHECK ( <replaceable class="PARAMETER">expression</replaceable> ) | @@ -423,11 +423,10 @@ and <replaceable class="PARAMETER">table_constraint</replaceable> is: contain values that match values in the referenced column(s) of some row of the referenced table. If <replaceable class="parameter">refcolumn</replaceable> is omitted, the - primary key of the <replaceable - class="parameter">reftable</replaceable> is used. The - referenced columns must be the columns of a unique or primary - key constraint in the referenced table. Note that foreign key - constraints cannot be defined between temporary tables and + primary key of the <replaceable class="parameter">reftable</replaceable> + is used. The referenced columns must be the columns of a non-deferrable + unique or primary key constraint in the referenced table. Note that + foreign key constraints cannot be defined between temporary tables and permanent tables. </para> @@ -534,9 +533,11 @@ and <replaceable class="PARAMETER">table_constraint</replaceable> is: after every command. Checking of constraints that are deferrable can be postponed until the end of the transaction (using the <xref linkend="sql-set-constraints" endterm="sql-set-constraints-title"> command). - <literal>NOT DEFERRABLE</literal> is the default. Only foreign - key constraints currently accept this clause. All other - constraint types are not deferrable. + <literal>NOT DEFERRABLE</literal> is the default. + Currently, only <literal>UNIQUE</>, <literal>PRIMARY KEY</>, and + <literal>REFERENCES</> (foreign key) constraints accept this + clause. <literal>NOT NULL</> and <literal>CHECK</> constraints are not + deferrable. </para> </listitem> </varlistentry> @@ -1141,6 +1142,23 @@ CREATE TABLE cinemas ( </refsect2> <refsect2> + <title>Non-deferred Uniqueness Constraints</title> + + <para> + When a <literal>UNIQUE</> or <literal>PRIMARY KEY</> constraint is + not deferrable, <productname>PostgreSQL</productname> checks for + uniqueness immediately whenever a row is inserted or modified. + The SQL standard says that uniqueness should be enforced only at + the end of the statement; this makes a difference when, for example, + a single command updates multiple key values. To obtain + standard-compliant behavior, declare the constraint as + <literal>DEFERRABLE</> but not deferred (i.e., <literal>INITIALLY + IMMEDIATE</>). Be aware that this can be significantly slower than + immediate uniqueness checking. + </para> + </refsect2> + + <refsect2> <title>Column Check Constraints</title> <para> |