ok

Mini Shell

Direktori : /opt/alt/postgresql11/usr/share/doc/alt-postgresql11-9.2.24/html/
Upload File :
Current File : //opt/alt/postgresql11/usr/share/doc/alt-postgresql11-9.2.24/html/indexes-collations.html

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<HTML
><HEAD
><TITLE
>Indexes and Collations</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK
REV="MADE"
HREF="mailto:pgsql-docs@postgresql.org"><LINK
REL="HOME"
TITLE="PostgreSQL 9.2.24 Documentation"
HREF="index.html"><LINK
REL="UP"
TITLE="Indexes"
HREF="indexes.html"><LINK
REL="PREVIOUS"
TITLE="Operator Classes and Operator Families"
HREF="indexes-opclass.html"><LINK
REL="NEXT"
TITLE="Examining Index Usage"
HREF="indexes-examine.html"><LINK
REL="STYLESHEET"
TYPE="text/css"
HREF="stylesheet.css"><META
HTTP-EQUIV="Content-Type"
CONTENT="text/html; charset=ISO-8859-1"><META
NAME="creation"
CONTENT="2017-11-06T22:43:11"></HEAD
><BODY
CLASS="SECT1"
><DIV
CLASS="NAVHEADER"
><TABLE
SUMMARY="Header navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="5"
ALIGN="center"
VALIGN="bottom"
><A
HREF="index.html"
>PostgreSQL 9.2.24 Documentation</A
></TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="top"
><A
TITLE="Operator Classes and Operator Families"
HREF="indexes-opclass.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="top"
><A
HREF="indexes.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="60%"
ALIGN="center"
VALIGN="bottom"
>Chapter 11. Indexes</TD
><TD
WIDTH="20%"
ALIGN="right"
VALIGN="top"
><A
TITLE="Examining Index Usage"
HREF="indexes-examine.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="INDEXES-COLLATIONS"
>11.10. Indexes and Collations</A
></H1
><P
>   An index can support only one collation per index column.
   If multiple collations are of interest, multiple indexes may be needed.
  </P
><P
>   Consider these statements:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE TABLE test1c (
    id integer,
    content varchar COLLATE "x"
);

CREATE INDEX test1c_content_index ON test1c (content);</PRE
><P>
   The index automatically uses the collation of the
   underlying column.  So a query of the form
</P><PRE
CLASS="PROGRAMLISTING"
>SELECT * FROM test1c WHERE content &gt; <TT
CLASS="REPLACEABLE"
><I
>constant</I
></TT
>;</PRE
><P>
   could use the index, because the comparison will by default use the
   collation of the column.  However, this index cannot accelerate queries
   that involve some other collation.  So if queries of the form, say,
</P><PRE
CLASS="PROGRAMLISTING"
>SELECT * FROM test1c WHERE content &gt; <TT
CLASS="REPLACEABLE"
><I
>constant</I
></TT
> COLLATE "y";</PRE
><P>
   are also of interest, an additional index could be created that supports
   the <TT
CLASS="LITERAL"
>"y"</TT
> collation, like this:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE INDEX test1c_content_y_index ON test1c (content COLLATE "y");</PRE
><P>
  </P
></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-opclass.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-examine.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Operator Classes and Operator Families</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="indexes.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>Examining Index Usage</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>

Zerion Mini Shell 1.0