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Change ON UPDATE SET NULL/SET DEFAULT referential actions to meet SQL spec.

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Previously, when executing an ON UPDATE SET NULL or SET DEFAULT action for
a multicolumn MATCH SIMPLE foreign key constraint, we would set only those
referencing columns corresponding to referenced columns that were changed.
This is what the SQL92 standard said to do --- but more recent versions
of the standard say that all referencing columns should be set to null or
their default values, no matter exactly which referenced columns changed.
At least for SET DEFAULT, that is clearly saner behavior.  It's somewhat
debatable whether it's an improvement for SET NULL, but it appears that
other RDBMS systems read the spec this way.  So let's do it like that.

This is a release-notable behavioral change, although considering that
our documentation already implied it was done this way, the lack of
complaints suggests few people use such cases.
This commit is contained in:
Tom Lane
2012-06-18 12:12:52 -04:00
parent f5297bdfe4
commit c75be2ad60
5 changed files with 72 additions and 218 deletions
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28
doc/src/sgml/ref/create_table.sgml
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@@ -585,8 +585,8 @@ CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXI
These clauses specify a foreign key constraint, which requires
that a group of one or more columns of the new table must only
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
column(s) of some row of the referenced table. If the <replaceable
class="parameter">refcolumn</replaceable> list is omitted, the
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
@@ -599,12 +599,16 @@ CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXI
values of the referenced table and referenced columns using the
given match type. There are three match types: <literal>MATCH
FULL</>, <literal>MATCH PARTIAL</>, and <literal>MATCH
SIMPLE</literal>, which is also the default. <literal>MATCH
SIMPLE</literal> (which is the default). <literal>MATCH
FULL</> will not allow one column of a multicolumn foreign key
to be null unless all foreign key columns are null.
<literal>MATCH SIMPLE</literal> allows some foreign key columns
to be null while other parts of the foreign key are not
null. <literal>MATCH PARTIAL</> is not yet implemented.
to be null unless all foreign key columns are null; if they are all
null, the row is not required to have a match in the referenced table.
<literal>MATCH SIMPLE</literal> allows any of the foreign key columns
to be null; if any of them are null, the row is not required to have a
match in the referenced table.
<literal>MATCH PARTIAL</> is not yet implemented.
(Of course, <literal>NOT NULL</> constraints can be applied to the
referencing column(s) to prevent these cases from arising.)
</para>
<para>
@@ -652,8 +656,8 @@ CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXI
<listitem>
<para>
Delete any rows referencing the deleted row, or update the
value of the referencing column to the new value of the
referenced column, respectively.
values of the referencing column(s) to the new values of the
referenced columns, respectively.
</para>
</listitem>
</varlistentry>
@@ -672,6 +676,8 @@ CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXI
<listitem>
<para>
Set the referencing column(s) to their default values.
(There must be a row in the referenced table matching the default
values, if they are not null, or the operation will fail.)
</para>
</listitem>
</varlistentry>
@@ -680,8 +686,8 @@ CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXI
<para>
If the referenced column(s) are changed frequently, it might be wise to
add an index to the foreign key column so that referential actions
associated with the foreign key column can be performed more
add an index to the referencing column(s) so that referential actions
associated with the foreign key constraint can be performed more
efficiently.
</para>
</listitem>