Programming the Perl DBI

Name

do

Synopsis

$rc  = $dbh->do($statement)           || die $dbh->errstr;
$rc  = $dbh->do($statement, \%attr)   || die $dbh->errstr;
$rv  = $dbh->do($statement, \%attr, @bind_values) || ...

Prepares and executes a single statement. Returns the number of rows affected or undef on error. A return value of -1 means the number of rows is not known or is not available.

This method is typically most useful for non-SELECT statements that either cannot be prepared in advance (due to a limitation of the driver) or do not need to be executed repeatedly. It should not be used for SELECT statements because it does not return a statement handle (so you can’t fetch any data).

The default do method is logically similar to:

sub do {
    my($dbh, $statement, $attr, @bind_values) = @_;
    my $sth = $dbh->prepare($statement, $attr) or return undef;
    $sth->execute(@bind_values) or return undef;
    my $rows = $sth->rows;
    ($rows == 0) ? "0E0" : $rows; # always return true if no error
}

For example:

my $rows_deleted = $dbh->do(q{
    DELETE FROM table
    WHERE status = ?
}, undef, 'DONE') || die $dbh->errstr;

Using placeholders and @bind_values with the do method can be useful because it avoids the need to correctly quote any variables in the $statement. But if you’ll be executing the statement many times, then it’s more efficient to prepare it once and call execute many times instead.

The q{...} style quoting used in this example avoids clashing with quotes that may be used in the SQL statement. Use the double-quote-like qq{...} operator ...