diff options
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/ddl.sgml | 18 | ||||
| -rw-r--r-- | doc/src/sgml/ref/create_table.sgml | 48 |
2 files changed, 37 insertions, 29 deletions
diff --git a/doc/src/sgml/ddl.sgml b/doc/src/sgml/ddl.sgml index 547c6e57de4..f50c6e47825 100644 --- a/doc/src/sgml/ddl.sgml +++ b/doc/src/sgml/ddl.sgml @@ -1,4 +1,4 @@ -<!-- $PostgreSQL: pgsql/doc/src/sgml/ddl.sgml,v 1.30 2004/08/08 21:33:11 tgl Exp $ --> +<!-- $PostgreSQL: pgsql/doc/src/sgml/ddl.sgml,v 1.31 2004/10/21 21:33:59 tgl Exp $ --> <chapter id="ddl"> <title>Data Definition</title> @@ -940,11 +940,17 @@ CREATE TABLE order_items ( <para> Restricting and cascading deletes are the two most common options. - <literal>RESTRICT</literal> can also be written as <literal>NO - ACTION</literal> and it's also the default if you do not specify - anything. There are two other options for what should happen with - the foreign key columns when a primary key is deleted: + <literal>RESTRICT</literal> prevents a statement from deleting a + referenced row. <literal>NO ACTION</literal> means that if any + referencing rows still exist when the constraint is checked, an error + is raised; this is the default if you do not specify anything. + (The essential difference between these choices is that + <literal>NO ACTION</literal> allows the check to be deferred until + later in the transaction, whereas <literal>RESTRICT</literal> does not.) + There are two other options: <literal>SET NULL</literal> and <literal>SET DEFAULT</literal>. + These cause the referencing columns to be set to nulls or default + values, respectively, when the referenced row is deleted. Note that these do not excuse you from observing any constraints. For example, if an action specifies <literal>SET DEFAULT</literal> but the default value would not satisfy the foreign key, the @@ -964,7 +970,7 @@ CREATE TABLE order_items ( <para> Finally, we should mention that a foreign key must reference - columns that are either a primary key or form a unique constraint. + columns that either are a primary key or form a unique constraint. If the foreign key references a unique constraint, there are some additional possibilities regarding how null values are matched. These are explained in the reference documentation for diff --git a/doc/src/sgml/ref/create_table.sgml b/doc/src/sgml/ref/create_table.sgml index 36396f62ace..e70f0c3dfd0 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 1.84 2004/08/02 04:25:31 tgl Exp $ +$PostgreSQL: pgsql/doc/src/sgml/ref/create_table.sgml,v 1.85 2004/10/21 21:33:59 tgl Exp $ PostgreSQL documentation --> @@ -417,12 +417,10 @@ and <replaceable class="PARAMETER">table_constraint</replaceable> is: <listitem> <para> - Theses clauses specify a foreign key constraint, which specifies + 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 which match against values in the referenced - column(s) <replaceable class="parameter">refcolumn</replaceable> - of the referenced table <replaceable - class="parameter">reftable</replaceable>. If <replaceable + 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 @@ -431,7 +429,7 @@ and <replaceable class="PARAMETER">table_constraint</replaceable> is: </para> <para> - A value inserted into these columns is matched against the + A value inserted into the referencing column(s) is matched against the 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 @@ -452,7 +450,9 @@ and <replaceable class="PARAMETER">table_constraint</replaceable> is: 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. There are the following possible + changed, no action is done. Referential actions apart from the + check of <literal>NO ACTION</literal> can not be deferred even if + the constraint is deferrable. There are the following possible actions for each clause: <variablelist> @@ -461,8 +461,10 @@ and <replaceable class="PARAMETER">table_constraint</replaceable> is: <listitem> <para> Produce an error indicating that the deletion or update - would create a foreign key constraint violation. This is - the default action. + would create a foreign key constraint violation. + If the constraint is deferred, this + error will be produced at constraint check time if there still + exist any referencing rows. This is the default action. </para> </listitem> </varlistentry> @@ -471,9 +473,10 @@ and <replaceable class="PARAMETER">table_constraint</replaceable> is: <term><literal>RESTRICT</literal></term> <listitem> <para> - Same as <literal>NO ACTION</literal> except that this action - will not be deferred even if the rest of the constraint is - deferrable and deferred. + 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. </para> </listitem> </varlistentry> @@ -493,7 +496,7 @@ and <replaceable class="PARAMETER">table_constraint</replaceable> is: <term><literal>SET NULL</literal></term> <listitem> <para> - Set the referencing column values to null. + Set the referencing column(s) to null. </para> </listitem> </varlistentry> @@ -502,7 +505,7 @@ and <replaceable class="PARAMETER">table_constraint</replaceable> is: <term><literal>SET DEFAULT</literal></term> <listitem> <para> - Set the referencing column values to their default value. + Set the referencing column(s) to their default values. </para> </listitem> </varlistentry> @@ -510,11 +513,10 @@ and <replaceable class="PARAMETER">table_constraint</replaceable> is: </para> <para> - If primary key column is updated frequently, it may be wise to - add an index to the foreign key column so that <literal>NO - ACTION</literal> and <literal>CASCADE</literal> actions - associated with the foreign key column can be more efficiently - performed. + If the referenced column(s) are changed frequently, it may 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 + efficiently. </para> </listitem> </varlistentry> @@ -844,9 +846,9 @@ CREATE TABLE distributors ( <programlisting> CREATE TABLE cinemas ( - id serial, - name text, - location text + id serial, + name text, + location text ) TABLESPACE diskvol1; </programlisting> </para> |