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><H1
><A
NAME="ECPG-SQL-GET-DESCRIPTOR"
></A
>GET DESCRIPTOR</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN45488"
></A
><H2
>Name</H2
>GET DESCRIPTOR -- get information from an SQL descriptor area</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN45491"
></A
><H2
>Synopsis</H2
><PRE
CLASS="SYNOPSIS"
>GET DESCRIPTOR <TT
CLASS="REPLACEABLE"
><I
>descriptor_name</I
></TT
> <TT
CLASS="REPLACEABLE"
><I
>:cvariable</I
></TT
> = <TT
CLASS="REPLACEABLE"
><I
>descriptor_header_item</I
></TT
> [, ... ]
GET DESCRIPTOR <TT
CLASS="REPLACEABLE"
><I
>descriptor_name</I
></TT
> VALUE <TT
CLASS="REPLACEABLE"
><I
>column_number</I
></TT
> <TT
CLASS="REPLACEABLE"
><I
>:cvariable</I
></TT
> = <TT
CLASS="REPLACEABLE"
><I
>descriptor_item</I
></TT
> [, ... ]</PRE
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN45500"
></A
><H2
>Description</H2
><P
> <TT
CLASS="COMMAND"
>GET DESCRIPTOR</TT
> retrieves information about a
query result set from an SQL descriptor area and stores it into
host variables. A descriptor area is typically populated
using <TT
CLASS="COMMAND"
>FETCH</TT
> or <TT
CLASS="COMMAND"
>SELECT</TT
>
before using this command to transfer the information into host
language variables.
</P
><P
> This command has two forms: The first form retrieves
descriptor <SPAN
CLASS="QUOTE"
>"header"</SPAN
> items, which apply to the result
set in its entirety. One example is the row count. The second
form, which requires the column number as additional parameter,
retrieves information about a particular column. Examples are
the column name and the actual column value.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN45508"
></A
><H2
>Parameters</H2
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="REPLACEABLE"
><I
>descriptor_name</I
></TT
></DT
><DD
><P
> A descriptor name.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>descriptor_header_item</I
></TT
></DT
><DD
><P
> A token identifying which header information item to retrieve.
Only <TT
CLASS="LITERAL"
>COUNT</TT
>, to get the number of columns in the
result set, is currently supported.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>column_number</I
></TT
></DT
><DD
><P
> The number of the column about which information is to be
retrieved. The count starts at 1.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>descriptor_item</I
></TT
></DT
><DD
><P
> A token identifying which item of information about a column
to retrieve. See <A
HREF="ecpg-descriptors.html#ECPG-NAMED-DESCRIPTORS"
>Section 33.7.1</A
> for
a list of supported items.
</P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>cvariable</I
></TT
></DT
><DD
><P
> A host variable that will receive the data retrieved from the
descriptor area.
</P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN45538"
></A
><H2
>Examples</H2
><P
> An example to retrieve the number of columns in a result set:
</P><PRE
CLASS="PROGRAMLISTING"
>EXEC SQL GET DESCRIPTOR d :d_count = COUNT;</PRE
><P>
</P
><P
> An example to retrieve a data length in the first column:
</P><PRE
CLASS="PROGRAMLISTING"
>EXEC SQL GET DESCRIPTOR d VALUE 1 :d_returned_octet_length = RETURNED_OCTET_LENGTH;</PRE
><P>
</P
><P
> An example to retrieve the data body of the second column as a
string:
</P><PRE
CLASS="PROGRAMLISTING"
>EXEC SQL GET DESCRIPTOR d VALUE 2 :d_data = DATA;</PRE
><P>
</P
><P
> Here is an example for a whole procedure of
executing <TT
CLASS="LITERAL"
>SELECT current_database();</TT
> and showing the number of
columns, the column data length, and the column data:
</P><PRE
CLASS="PROGRAMLISTING"
>int
main(void)
{
EXEC SQL BEGIN DECLARE SECTION;
int d_count;
char d_data[1024];
int d_returned_octet_length;
EXEC SQL END DECLARE SECTION;
EXEC SQL CONNECT TO testdb AS con1 USER testuser;
EXEC SQL ALLOCATE DESCRIPTOR d;
/* Declare, open a cursor, and assign a descriptor to the cursor */
EXEC SQL DECLARE cur CURSOR FOR SELECT current_database();
EXEC SQL OPEN cur;
EXEC SQL FETCH NEXT FROM cur INTO SQL DESCRIPTOR d;
/* Get a number of total columns */
EXEC SQL GET DESCRIPTOR d :d_count = COUNT;
printf("d_count = %d\n", d_count);
/* Get length of a returned column */
EXEC SQL GET DESCRIPTOR d VALUE 1 :d_returned_octet_length = RETURNED_OCTET_LENGTH;
printf("d_returned_octet_length = %d\n", d_returned_octet_length);
/* Fetch the returned column as a string */
EXEC SQL GET DESCRIPTOR d VALUE 1 :d_data = DATA;
printf("d_data = %s\n", d_data);
/* Closing */
EXEC SQL CLOSE cur;
EXEC SQL COMMIT;
EXEC SQL DEALLOCATE DESCRIPTOR d;
EXEC SQL DISCONNECT ALL;
return 0;
}</PRE
><P>
When the example is executed, the result will look like this:
</P><PRE
CLASS="SCREEN"
>d_count = 1
d_returned_octet_length = 6
d_data = testdb</PRE
><P>
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN45550"
></A
><H2
>Compatibility</H2
><P
> <TT
CLASS="COMMAND"
>GET DESCRIPTOR</TT
> is specified in the SQL standard.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN45554"
></A
><H2
>See Also</H2
><A
HREF="ecpg-sql-allocate-descriptor.html"
>ALLOCATE DESCRIPTOR</A
>, <A
HREF="ecpg-sql-set-descriptor.html"
>SET DESCRIPTOR</A
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