Sophie

Sophie

distrib > Mandriva > 2008.1 > x86_64 > media > main-testing > by-pkgid > bab02a23fa9f3df8d66a9a3231b50245 > files > 55

postgresql8.3-docs-8.3.6-2mdv2008.1.x86_64.rpm

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<HTML
><HEAD
><TITLE
>pg_cast</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 8.3.6 Documentation"
HREF="index.html"><LINK
REL="UP"
TITLE="System Catalogs"
HREF="catalogs.html"><LINK
REL="PREVIOUS"
TITLE="pg_autovacuum"
HREF="catalog-pg-autovacuum.html"><LINK
REL="NEXT"
TITLE="pg_class"
HREF="catalog-pg-class.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="2009-02-03T04:34:16"></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"
>PostgreSQL 8.3.6 Documentation</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="top"
><A
HREF="catalog-pg-autovacuum.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="top"
><A
HREF="catalogs.html"
>Fast Backward</A
></TD
><TD
WIDTH="60%"
ALIGN="center"
VALIGN="bottom"
>Chapter 44. System Catalogs</TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="top"
><A
HREF="catalogs.html"
>Fast Forward</A
></TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="top"
><A
HREF="catalog-pg-class.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="CATALOG-PG-CAST"
>44.11. <TT
CLASS="STRUCTNAME"
>pg_cast</TT
></A
></H1
><A
NAME="AEN68974"
></A
><P
>   The catalog <TT
CLASS="STRUCTNAME"
>pg_cast</TT
> stores data type conversion
   paths, both built-in paths and those defined with
   <A
HREF="sql-createcast.html"
><I
>CREATE CAST</I
></A
>.
  </P
><P
>   It should be noted that <TT
CLASS="STRUCTNAME"
>pg_cast</TT
> does not represent
   every type conversion that the system knows how to perform; only those that
   cannot be deduced from some generic rule.  For example, casting between a
   domain and its base type is not explicitly represented in
   <TT
CLASS="STRUCTNAME"
>pg_cast</TT
>.  Another important exception is that
   <SPAN
CLASS="QUOTE"
>"I/O conversion casts"</SPAN
>, those performed using a data type's own
   I/O functions to convert to or from <TT
CLASS="TYPE"
>text</TT
> or other string types,
   are not explicitly represented in <TT
CLASS="STRUCTNAME"
>pg_cast</TT
>.
  </P
><DIV
CLASS="TABLE"
><A
NAME="AEN68985"
></A
><P
><B
>Table 44-11. <TT
CLASS="STRUCTNAME"
>pg_cast</TT
> Columns</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><COL><COL><THEAD
><TR
><TH
>Name</TH
><TH
>Type</TH
><TH
>References</TH
><TH
>Description</TH
></TR
></THEAD
><TBODY
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>castsource</TT
></TD
><TD
><TT
CLASS="TYPE"
>oid</TT
></TD
><TD
><TT
CLASS="LITERAL"
><A
HREF="catalog-pg-type.html"
><TT
CLASS="STRUCTNAME"
>pg_type</TT
></A
>.oid</TT
></TD
><TD
>OID of the source data type</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>casttarget</TT
></TD
><TD
><TT
CLASS="TYPE"
>oid</TT
></TD
><TD
><TT
CLASS="LITERAL"
><A
HREF="catalog-pg-type.html"
><TT
CLASS="STRUCTNAME"
>pg_type</TT
></A
>.oid</TT
></TD
><TD
>OID of the target data type</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>castfunc</TT
></TD
><TD
><TT
CLASS="TYPE"
>oid</TT
></TD
><TD
><TT
CLASS="LITERAL"
><A
HREF="catalog-pg-proc.html"
><TT
CLASS="STRUCTNAME"
>pg_proc</TT
></A
>.oid</TT
></TD
><TD
>       The OID of the function to use to perform this cast.  Zero is
       stored if the data types are binary compatible (that is, no
       run-time operation is needed to perform the cast)
      </TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>castcontext</TT
></TD
><TD
><TT
CLASS="TYPE"
>char</TT
></TD
><TD
>&nbsp;</TD
><TD
>       Indicates what contexts the cast can be invoked in.
       <TT
CLASS="LITERAL"
>e</TT
> means only as an explicit cast (using
       <TT
CLASS="LITERAL"
>CAST</TT
> or <TT
CLASS="LITERAL"
>::</TT
> syntax).
       <TT
CLASS="LITERAL"
>a</TT
> means implicitly in assignment
       to a target column, as well as explicitly.
       <TT
CLASS="LITERAL"
>i</TT
> means implicitly in expressions, as well as the
       other cases
      </TD
></TR
></TBODY
></TABLE
></DIV
><P
>   The cast functions listed in <TT
CLASS="STRUCTNAME"
>pg_cast</TT
> must
   always take the cast source type as their first argument type, and
   return the cast destination type as their result type.  A cast
   function can have up to three arguments.  The second argument,
   if present, must be type <TT
CLASS="TYPE"
>integer</TT
>; it receives the type
   modifier associated with the destination type, or <TT
CLASS="LITERAL"
>-1</TT
>
   if there is none.  The third argument,
   if present, must be type <TT
CLASS="TYPE"
>boolean</TT
>; it receives <TT
CLASS="LITERAL"
>true</TT
>
   if the cast is an explicit cast, <TT
CLASS="LITERAL"
>false</TT
> otherwise.
  </P
><P
>   It is legitimate to create a <TT
CLASS="STRUCTNAME"
>pg_cast</TT
> entry
   in which the source and target types are the same, if the associated
   function takes more than one argument.  Such entries represent
   <SPAN
CLASS="QUOTE"
>"length coercion functions"</SPAN
> that coerce values of the type
   to be legal for a particular type modifier value.
  </P
><P
>   When a <TT
CLASS="STRUCTNAME"
>pg_cast</TT
> entry has different source and
   target types and a function that takes more than one argument, it
   represents converting from one type to another and applying a length
   coercion in a single step.  When no such entry is available, coercion
   to a type that uses a type modifier involves two steps, one to
   convert between data types and a second to apply the modifier.
  </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="catalog-pg-autovacuum.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="catalog-pg-class.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><TT
CLASS="STRUCTNAME"
>pg_autovacuum</TT
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="catalogs.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><TT
CLASS="STRUCTNAME"
>pg_class</TT
></TD
></TR
></TABLE
></DIV
></BODY
></HTML
>