diff options
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/ddl.sgml | 20 | ||||
| -rw-r--r-- | doc/src/sgml/ref/create_table.sgml | 19 |
2 files changed, 23 insertions, 16 deletions
diff --git a/doc/src/sgml/ddl.sgml b/doc/src/sgml/ddl.sgml index 440a899d122..11fa9c4a327 100644 --- a/doc/src/sgml/ddl.sgml +++ b/doc/src/sgml/ddl.sgml @@ -1181,16 +1181,16 @@ CREATE TABLE posts ( <para> A foreign key must reference columns that either are a primary key or - form a unique constraint. This means that the referenced columns always - have an index (the one underlying the primary key or unique constraint); - so checks on whether a referencing row has a match will be efficient. - Since a <command>DELETE</command> of a row from the referenced table - or an <command>UPDATE</command> of a referenced column will require - a scan of the referencing table for rows matching the old value, it - is often a good idea to index the referencing columns too. Because this - is not always needed, and there are many choices available on how - to index, declaration of a foreign key constraint does not - automatically create an index on the referencing columns. + form a unique constraint, or are columns from a non-partial unique index. + This means that the referenced columns always have an index to allow + efficient lookups on whether a referencing row has a match. Since a + <command>DELETE</command> of a row from the referenced table or an + <command>UPDATE</command> of a referenced column will require a scan of + the referencing table for rows matching the old value, it is often a good + idea to index the referencing columns too. Because this is not always + needed, and there are many choices available on how to index, the + declaration of a foreign key constraint does not automatically create an + index on the referencing columns. </para> <para> diff --git a/doc/src/sgml/ref/create_table.sgml b/doc/src/sgml/ref/create_table.sgml index 10ef699fab9..6a15676d882 100644 --- a/doc/src/sgml/ref/create_table.sgml +++ b/doc/src/sgml/ref/create_table.sgml @@ -1137,10 +1137,11 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM 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. The user - must have <literal>REFERENCES</literal> permission on the referenced table - (either the whole table, or the specific referenced columns). The + is used. Otherwise, the <replaceable class="parameter">refcolumn</replaceable> + list must refer to the columns of a non-deferrable unique or primary key + constraint or be the columns of a non-partial unique index. The user + must have <literal>REFERENCES</literal> permission on the referenced + table (either the whole table, or the specific referenced columns). The addition of a foreign key constraint requires a <literal>SHARE ROW EXCLUSIVE</literal> lock on the referenced table. Note that foreign key constraints cannot be defined between temporary @@ -2277,13 +2278,19 @@ CREATE TABLE cities_partdef </refsect2> <refsect2> - <title>Foreign-Key Constraint Actions</title> + <title>Foreign Key Constraints</title> <para> - The ability to specify column lists in the foreign-key actions + The ability to specify column lists in the foreign key actions <literal>SET DEFAULT</literal> and <literal>SET NULL</literal> is a <productname>PostgreSQL</productname> extension. </para> + + <para> + It is a <productname>PostgreSQL</productname> extension that a + foreign key constraint may reference columns of a unique index instead of + columns of a primary key or unique constraint. + </para> </refsect2> <refsect2> |