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55 <chapter id="datatype">
@@ -654,10 +654,11 @@ NUMERIC
654654 </indexterm>
655655
656656 <para>
657- The <type>serial</type> data types are not truly types, but are a
658- notational convenience for setting up unique identifier columns
659- in tables.
660- In the current implementation, specifying
657+ The <type>serial</type> data type is not a true type, but merely
658+ a notational convenience for setting up identifier columns
659+ (similar to the <literal>AUTO_INCREMENT</literal> property
660+ supported by some other databases). In the current
661+ implementation, specifying
661662
662663<programlisting>
663664CREATE TABLE <replaceable class="parameter">tablename</replaceable> (
@@ -683,33 +684,50 @@ CREATE TABLE <replaceable class="parameter">tablename</replaceable> (
683684 not automatic.
684685 </para>
685686
687+ <para>
688+ To use a <type>serial</type> column to insert the next value of
689+ the sequence into the table, specify that the <type>serial</type>
690+ column should be assigned the default value. This can be done
691+ either be excluding from the column from the list of columns in
692+ the <command>INSERT</command> statement, or through the use of
693+ the <literal>DEFAULT</literal> keyword.
694+ </para>
695+
686696 <para>
687697 The type names <type>serial</type> and <type>serial4</type> are
688698 equivalent: both create <type>integer</type> columns. The type
689699 names <type>bigserial</type> and <type>serial8</type> work just
690700 the same way, except that they create a <type>bigint</type>
691701 column. <type>bigserial</type> should be used if you anticipate
692- the use of more than 2<superscript>31</> identifiers over the lifetime of the table.
702+ the use of more than 2<superscript>31</> identifiers over the
703+ lifetime of the table.
693704 </para>
694705
695706 <para>
696- The sequence created by a <type>serial</type> type is automatically
697- dropped when
698- the owning column is dropped, and cannot be dropped otherwise.
699- (This was not true in <productname>PostgreSQL</productname> releases
700- before 7.3. Note that this automatic drop linkage will not occur for a
701- sequence created by reloading a dump from a pre-7.3 database; the dump
702- file does not contain the information needed to establish the dependency
703- link.)
707+ The sequence created by a <type>serial</type> type is
708+ automatically dropped when the owning column is dropped, and
709+ cannot be dropped otherwise. (This was not true in
710+ <productname>PostgreSQL</productname> releases before 7.3. Note
711+ that this automatic drop linkage will not occur for a sequence
712+ created by reloading a dump from a pre-7.3 database; the dump
713+ file does not contain the information needed to establish the
714+ dependency link.) Furthermore, this dependency between sequence
715+ and column is made only for the <type>serial</> column itself; if
716+ any other columns reference the sequence (perhaps by manually
717+ calling the <function>nextval()</>) function), they may be broken
718+ if the sequence is removed. Using <type>serial</> columns in
719+ fashion is considered bad form.
704720 </para>
705721
706- <note><para>
707- Prior to <productname>PostgreSQL</productname> 7.3, <type>serial</type>
708- implied <literal>UNIQUE</literal>. This is no longer automatic. If
709- you wish a serial column to be <literal>UNIQUE</literal> or a
710- <literal>PRIMARY KEY</literal> it must now be specified, same as with
711- any other data type.
712- </para></note>
722+ <note>
723+ <para>
724+ Prior to <productname>PostgreSQL</> 7.3, <type>serial</type>
725+ implied <literal>UNIQUE</literal>. This is no longer automatic.
726+ If you wish a serial column to be <literal>UNIQUE</literal> or a
727+ <literal>PRIMARY KEY</literal> it must now be specified, just as
728+ with any other data type.
729+ </para>
730+ </note>
713731 </sect2>
714732 </sect1>
715733