Programming the Perl DBI

Statement Handle Attributes or Statement Metadata

Statement handle attributes are specific to statement handles, and inherit any inheritable attributes from their parent database handle. Many statement handle attributes are defined as being read-only because they simply describe the prepared statement or its results.

In theoretical terms, these attributes should be defined when the statement handle is prepared, but in practical terms, you should only rely on the attribute values after the statement handle has been both prepared and executed. Similarly, with a few drivers, fetching all the data from a SELECT statement or explicitly invoking the finish() method against a statement handle may cause the values of the statement handle attributes to be no longer available.

The DBI specification in Appendix A provides a complete list of all the statement handle attributes defined within the DBI.

Statement

This attribute contains the statement string passed to the prepare() method.

NUM_OF_FIELDS

This attribute is set to contain the number of columns that will be returned by a SELECT statement. For example:

$sth = $dbh->prepare( "
            SELECT name, location, mapref
            FROM megaliths
          " );
$sth->execute();
print "SQL statement contains $sth->{NUM_OF_FIELDS} columns\n";

Non-SELECT statements will contain the attribute value of zero. This allows you to quickly determine whether or not the statement is a SELECT statement.

NAME NAME_uc NAME_lc

The NAME attribute contains the names of the selected ...