Sophie: postgresql-docs-7.3.2-5mdk ppc

postgresql-docs-7.3.2-5mdk.ppc.rpm

<HTML
><HEAD
><TITLE
>Unique Indexes</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.73
"><LINK
REV="MADE"
HREF="mailto:pgsql-docs@postgresql.org"><LINK
REL="HOME"
TITLE="PostgreSQL 7.3.2 Documentation"
HREF="index.html"><LINK
REL="UP"
TITLE="Indexes"
HREF="indexes.html"><LINK
REL="PREVIOUS"
TITLE="Multicolumn Indexes"
HREF="indexes-multicolumn.html"><LINK
REL="NEXT"
TITLE="Functional Indexes"
HREF="indexes-functional.html"><LINK
REL="STYLESHEET"
TYPE="text/css"
HREF="stylesheet.css"><META
NAME="creation"
CONTENT="2003-02-03T20:17:34"></HEAD
><BODY
CLASS="SECT1"
BGCOLOR="#FFFFFF"
TEXT="#000000"
LINK="#0000FF"
VLINK="#840084"
ALINK="#0000FF"
><DIV
CLASS="NAVHEADER"
><TABLE
SUMMARY="Header navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="3"
ALIGN="center"
>PostgreSQL 7.3.2 Documentation</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="bottom"
><A
HREF="indexes-multicolumn.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="80%"
ALIGN="center"
VALIGN="bottom"
>Chapter 8. Indexes</TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="bottom"
><A
HREF="indexes-functional.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="INDEXES-UNIQUE"
>8.4. Unique Indexes</A
></H1
><A
NAME="AEN11153"
></A
><P
>   Indexes may also be used to enforce uniqueness of a column's value,
   or the uniqueness of the combined values of more than one column.
</P><PRE
CLASS="SYNOPSIS"
>CREATE UNIQUE INDEX <TT
CLASS="REPLACEABLE"
><I
>name</I
></TT
> ON <TT
CLASS="REPLACEABLE"
><I
>table</I
></TT
> (<TT
CLASS="REPLACEABLE"
><I
>column</I
></TT
> [<SPAN
CLASS="OPTIONAL"
>, ...</SPAN
>]);</PRE
><P>
   Currently, only B-tree indexes can be declared unique.
  </P
><P
>   When an index is declared unique, multiple table rows with equal
   indexed values will not be allowed.  NULL values are not considered
   equal.
  </P
><P
>   <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> automatically creates unique
   indexes when a table is declared with a unique constraint or a
   primary key, on the columns that make up the primary key or unique
   columns (a multicolumn index, if appropriate), to enforce that
   constraint.  A unique index can be added to a table at any later
   time, to add a unique constraint.
  </P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
>    The preferred way to add a unique constraint to a table is
    <TT
CLASS="LITERAL"
>ALTER TABLE ... ADD CONSTRAINT</TT
>.  The use of
    indexes to enforce unique constraints could be considered an
    implementation detail that should not be accessed directly.
   </P
></BLOCKQUOTE
></DIV
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
SUMMARY="Footer navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="indexes-multicolumn.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="index.html"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="indexes-functional.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Multicolumn Indexes</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="indexes.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>Functional Indexes</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>