<command>DESCRIBE</command> statement the <literal>DESCRIPTOR</literal>
    keyword can be completely omitted if the <literal>INTO</literal> keyword is used:
<programlisting>
EXEC SQL DESCRIBE prepared_statement INTO mysqlda;
</programlisting>
   </para>

    <procedure>
     <para>
      The general flow of a program that uses SQLDA is:
     </para>
     <step><simpara>Prepare a query, and declare a cursor for it.</simpara></step>
     <step><simpara>Declare an SQLDA for the result rows.</simpara></step>
     <step><simpara>Declare an SQLDA for the input parameters, and initialize them (memory allocation, parameter settings).</simpara></step>
     <step><simpara>Open a cursor with the input SQLDA.</simpara></step>
     <step><simpara>Fetch rows from the cursor, and store them into an output SQLDA.</simpara></step>
     <step><simpara>Read values from the output SQLDA into the host variables (with conversion if necessary).</simpara></step>
     <step><simpara>Close the cursor.</simpara></step>
     <step><simpara>Free the memory area allocated for the input SQLDA.</simpara></step>
    </procedure>

   <sect3 id="ecpg-sqlda-descriptors-sqlda">
    <title>SQLDA Data Structure</title>

    <para>
     SQLDA uses three data structure
     types: <type>sqlda_t</type>, <type>sqlvar_t</type>,
     and <type>struct sqlname</type>.
    </para>

    <tip>
     <para>
      PostgreSQL's SQLDA has a similar data structure to the one in
      IBM DB2 Universal Database, so some technical information on
      DB2's SQLDA could help understanding PostgreSQL's one better.
     </para>
    </tip>

    <sect4 id="ecpg-sqlda-sqlda">
     <title>sqlda_t Structure</title>

     <para>
      The structure type <type>sqlda_t</type> is the type of the
      actual SQLDA.  It holds one record.  And two or
      more <type>sqlda_t</type> structures can be connected in a
      linked list with the pointer in
      the <structfield>desc_next</structfield> field, thus
      representing an ordered collection of rows.  So, when two or
      more rows are fetched, the application can read them by
      following the <structfield>desc_next</structfield> pointer in
      each <type>sqlda_t</type> node.
     </para>

     <para>
      The definition of <type>sqlda_t</type> is:
<programlisting>
struct sqlda_struct
{
    char            sqldaid[8];
    long            sqldabc;
    short           sqln;
    short           sqld;
    struct sqlda_struct *desc_next;
    struct sqlvar_struct sqlvar[1];
};

typedef struct sqlda_struct sqlda_t;
</programlisting>

      The meaning of the fields is:

    <variablelist>
     <varlistentry id="ecpg-sqlda-sqlda-sqldaid">
      <term><literal>sqldaid</literal></term>
      <listitem>
       <para>
        It contains the literal string <literal>"SQLDA  "</literal>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="ecpg-sqlda-sqlda-sqldabc">
      <term><literal>sqldabc</literal></term>
      <listitem>
       <para>
        It contains the size of the allocated space in bytes.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="ecpg-sqlda-sqlda-sqln">
      <term><literal>sqln</literal></term>
      <listitem>
       <para>
        It contains the number of input parameters for a parameterized query in
        case it's passed into <command>OPEN</command>, <command>DECLARE</command> or
        <command>EXECUTE</command> statements using the <literal>USING</literal>
        keyword. In case it's used as output of <command>SELECT</command>,
        <command>EXECUTE</command> or <command>FETCH</command> statements,
        its value is the same as <literal>sqld</literal>
        statement
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="ecpg-sqlda-sqlda-sqld">
      <term><literal>sqld</literal></term>
      <listitem>
       <para>
        It contains the number of fields in a result set.
       </para>
      </listitem>
     </varlistentry>