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Diffstat (limited to 'doc/src/sgml/ddl.sgml')
| -rw-r--r-- | doc/src/sgml/ddl.sgml | 31 |
1 files changed, 29 insertions, 2 deletions
diff --git a/doc/src/sgml/ddl.sgml b/doc/src/sgml/ddl.sgml index 2504970a7e..6d29859ed9 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 1.35 2004/12/23 05:37:39 tgl Exp $ --> +<!-- $PostgreSQL: pgsql/doc/src/sgml/ddl.sgml,v 1.36 2005/01/08 01:44:05 tgl Exp $ --> <chapter id="ddl"> <title>Data Definition</title> @@ -395,7 +395,28 @@ CREATE TABLE products ( evaluated whenever the default value is inserted (<emphasis>not</emphasis> when the table is created). A common example is that a timestamp column may have a default of <literal>now()</>, - so that it gets set to the time of row insertion. + so that it gets set to the time of row insertion. Another common + example is generating a <quote>serial number</> for each row. + In <productname>PostgreSQL</productname> this is typically done by + something like +<programlisting> +CREATE TABLE products ( + product_no integer <emphasis>DEFAULT nextval('products_product_no_seq')</emphasis>, + ... +); +</programlisting> + where the <literal>nextval()</> function supplies successive values + from a <firstterm>sequence object</> (see <xref + linkend="functions-sequence">). This arrangement is sufficiently common + that there's a special shorthand for it: +<programlisting> +CREATE TABLE products ( + product_no <emphasis>SERIAL</emphasis>, + ... +); +</programlisting> + The <literal>SERIAL</> shorthand is discussed further in <xref + linkend="datatype-serial">. </para> </sect1> @@ -1139,6 +1160,12 @@ WHERE c.altitude > 500 and c.tableoid = p.oid; </para> <para> + A table can inherit from more than one parent table, in which case it has + the union of the columns defined by the parent tables (plus any columns + declared specifically for the child table). + </para> + + <para> A serious limitation of the inheritance feature is that indexes (including unique constraints) and foreign key constraints only apply to single tables, not to their inheritance children. This is true on both the |