my $sth = $dbh->prepare('SELECT name FROM user WHERE id = ?');

# generates query "SELECT name FROM user WHERE id = 1"
$sth->execute(1);

# generates query "SELECT name FROM user WHERE id = '1'"
$sth->execute('1');


##</code><code>##


my $sth = $dbh->prepare('SELECT name FROM user LIMIT ?');

# generates query "SELECT name FROM user LIMIT 1"
$sth->execute(1);

# generates ILLEGAL query "SELECT name FROM user LIMIT '1'"
$sth->execute('1');