database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-12-22 17:42:17 +03:00
Code Activity

Support deferrable uniqueness constraints.

Browse Source 
The current implementation fires an AFTER ROW trigger for each tuple that
looks like it might be non-unique according to the index contents at the
time of insertion.  This works well as long as there aren't many conflicts,
but won't scale to massive unique-key reassignments.  Improving that case
is a TODO item.

Dean Rasheed
This commit is contained in:
Tom Lane
2009-07-29 20:56:21 +00:00
parent 8504905793
commit 25d9bf2e3e
51 changed files with 1241 additions and 245 deletions
Download Patch File Download Diff File Expand all files Collapse all files

40
doc/src/sgml/ref/create_table.sgml
View File

@@ -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>
@@ -1140,6 +1141,23 @@ CREATE TABLE cinemas (
</para>
</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>