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doc: Improve description of referential actions

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Some of the differences between NO ACTION and RESTRICT were not
explained fully.

Discussion: https://www.postgresql.org/message-id/ea5b2777-266a-46fa-852f-6fca6ec480ad@eisentraut.org
This commit is contained in:
Peter Eisentraut
2024-11-29 08:52:28 +01:00
parent 4a2dbfc6be
commit 1e08905842
2 changed files with 44 additions and 17 deletions
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doc/src/sgml/ref/create_table.sgml
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@@ -1248,17 +1248,16 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
clause specifies the action to perform when a referenced column
in the referenced table is being updated to a new value. If the
row is updated, but the referenced column is not actually
changed, no action is done. Referential actions other than the
<literal>NO ACTION</literal> check cannot be deferred, even if
the constraint is declared deferrable. There are the following possible
actions for each clause:
changed, no action is done. Referential actions are executed as part of
the data changing command, even if the constraint is deferred. There
are the following possible actions for each clause:
<variablelist>
<varlistentry id="sql-createtable-parms-references-refact-no-action">
<term><literal>NO ACTION</literal></term>
<listitem>
<para>
Produce an error indicating that the deletion or update
Produce an error if the deletion or update
would create a foreign key constraint violation.
If the constraint is deferred, this
error will be produced at constraint check time if there still
@@ -1271,10 +1270,13 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
<term><literal>RESTRICT</literal></term>
<listitem>
<para>
Produce an error indicating that the deletion or update
would create a foreign key constraint violation.
This is the same as <literal>NO ACTION</literal> except that
the check is not deferrable.
Produce an error if a row to be deleted or updated matches a row in
the referencing table. This prevents the action even if the state
after the action would not violate the foreign key constraint. In
particular, it prevents updates of referenced rows to values that
are distinct but compare as equal. (But it does not prevent
<quote>no-op</quote> updates that update a column to the same
value.)
</para>
</listitem>
</varlistentry>