Sophie: postgresql8.3-docs-8.3.6-2mdv2008.1 x86

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
>Using SQL Descriptor Areas</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="ECPG - Embedded SQL in C"
HREF="ecpg.html"><LINK
REL="PREVIOUS"
TITLE="Informix compatibility mode"
HREF="ecpg-informix-compat.html"><LINK
REL="NEXT"
TITLE="Error Handling"
HREF="ecpg-errors.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="ecpg-informix-compat.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="top"
><A
HREF="ecpg.html"
>Fast Backward</A
></TD
><TD
WIDTH="60%"
ALIGN="center"
VALIGN="bottom"
>Chapter 32. <SPAN
CLASS="APPLICATION"
>ECPG</SPAN
> - Embedded <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> in C</TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="top"
><A
HREF="ecpg.html"
>Fast Forward</A
></TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="top"
><A
HREF="ecpg-errors.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="ECPG-DESCRIPTORS"
>32.10. Using SQL Descriptor Areas</A
></H1
><P
>   An SQL descriptor area is a more sophisticated method for
   processing the result of a <TT
CLASS="COMMAND"
>SELECT</TT
> or
   <TT
CLASS="COMMAND"
>FETCH</TT
> statement.  An SQL descriptor area groups
   the data of one row of data together with metadata items into one
   data structure.  The metadata is particularly useful when executing
   dynamic SQL statements, where the nature of the result columns might
   not be known ahead of time.
  </P
><P
>   An SQL descriptor area consists of a header, which contains
   information concerning the entire descriptor, and one or more item
   descriptor areas, which basically each describe one column in the
   result row.
  </P
><P
>   Before you can use an SQL descriptor area, you need to allocate one:
</P><PRE
CLASS="PROGRAMLISTING"
>EXEC SQL ALLOCATE DESCRIPTOR <TT
CLASS="REPLACEABLE"
><I
>identifier</I
></TT
>;</PRE
><P>
   The identifier serves as the <SPAN
CLASS="QUOTE"
>"variable name"</SPAN
> of the
   descriptor area.  
   When you don't need the descriptor anymore, you should deallocate
   it:
</P><PRE
CLASS="PROGRAMLISTING"
>EXEC SQL DEALLOCATE DESCRIPTOR <TT
CLASS="REPLACEABLE"
><I
>identifier</I
></TT
>;</PRE
><P>
  </P
><P
>   To use a descriptor area, specify it as the storage target in an
   <TT
CLASS="LITERAL"
>INTO</TT
> clause, instead of listing host variables:
</P><PRE
CLASS="PROGRAMLISTING"
>EXEC SQL FETCH NEXT FROM mycursor INTO DESCRIPTOR mydesc;</PRE
><P>
  </P
><P
>   Now how do you get the data out of the descriptor area?  You can
   think of the descriptor area as a structure with named fields.  To
   retrieve the value of a field from the header and store it into a
   host variable, use the following command:
</P><PRE
CLASS="PROGRAMLISTING"
>EXEC SQL GET DESCRIPTOR <TT
CLASS="REPLACEABLE"
><I
>name</I
></TT
> :<TT
CLASS="REPLACEABLE"
><I
>hostvar</I
></TT
> = <TT
CLASS="REPLACEABLE"
><I
>field</I
></TT
>;</PRE
><P>
   Currently, there is only one header field defined:
   <TT
CLASS="REPLACEABLE"
><I
>COUNT</I
></TT
>, which tells how many item
   descriptor areas exist (that is, how many columns are contained in
   the result).  The host variable needs to be of an integer type.  To
   get a field from the item descriptor area, use the following
   command:
</P><PRE
CLASS="PROGRAMLISTING"
>EXEC SQL GET DESCRIPTOR <TT
CLASS="REPLACEABLE"
><I
>name</I
></TT
> VALUE <TT
CLASS="REPLACEABLE"
><I
>num</I
></TT
> :<TT
CLASS="REPLACEABLE"
><I
>hostvar</I
></TT
> = <TT
CLASS="REPLACEABLE"
><I
>field</I
></TT
>;</PRE
><P>
   <TT
CLASS="REPLACEABLE"
><I
>num</I
></TT
> can be a literal integer or a host
   variable containing an integer. Possible fields are:

   <P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>CARDINALITY</TT
> (integer)</DT
><DD
><P
>       number of rows in the result set
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>DATA</TT
></DT
><DD
><P
>       actual data item (therefore, the data type of this field
       depends on the query)
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>DATETIME_INTERVAL_CODE</TT
> (integer)</DT
><DD
><P
>       ?
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>DATETIME_INTERVAL_PRECISION</TT
> (integer)</DT
><DD
><P
>       not implemented
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>INDICATOR</TT
> (integer)</DT
><DD
><P
>       the indicator (indicating a null value or a value truncation)
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>KEY_MEMBER</TT
> (integer)</DT
><DD
><P
>       not implemented
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>LENGTH</TT
> (integer)</DT
><DD
><P
>       length of the datum in characters
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>NAME</TT
> (string)</DT
><DD
><P
>       name of the column
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>NULLABLE</TT
> (integer)</DT
><DD
><P
>       not implemented
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>OCTET_LENGTH</TT
> (integer)</DT
><DD
><P
>       length of the character representation of the datum in bytes
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>PRECISION</TT
> (integer)</DT
><DD
><P
>       precision (for type <TT
CLASS="TYPE"
>numeric</TT
>)
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>RETURNED_LENGTH</TT
> (integer)</DT
><DD
><P
>       length of the datum in characters
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>RETURNED_OCTET_LENGTH</TT
> (integer)</DT
><DD
><P
>       length of the character representation of the datum in bytes
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>SCALE</TT
> (integer)</DT
><DD
><P
>       scale (for type <TT
CLASS="TYPE"
>numeric</TT
>)
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>TYPE</TT
> (integer)</DT
><DD
><P
>       numeric code of the data type of the column
      </P
></DD
></DL
></DIV
><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="ecpg-informix-compat.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="ecpg-errors.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><SPAN
CLASS="PRODUCTNAME"
>Informix</SPAN
> compatibility mode</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="ecpg.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>Error Handling</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>