my $statement = <<'__SQL__';
SELECT *
   FROM t_user_portal
   WHERE f_client = ?
__SQL__

my $sth = $dbh->prepare($statement)
     or die $dbh->errstr;

my $client='lanx';

my $rv = $sth->execute($client)
     or die $sth->errstr;

##</code><code>##

SELECT *
   FROM t_user_portal
   WHERE f_client = 'lanx'

##</code><code>##

PREPARE stmt1 FROM 'SELECT * FROM t_user_portal WHERE f_client = ?';
SET @client = 'lanx';
EXECUTE stmt1 USING @client;