[ASK] Check if record exist in database before submit form project

Need Help
1

How to check record exist in database?
when user click submit (form project), it must check 1 field in table database

<?php echo $this->Form->create() ?>
<?php echo $this->Form->input; ?>
if record not exist in field table biodata go to biodata else <?php echo $this->Form->submit(__l('Next'); ?>
<?php echo $this->Form->end();?>

what command can i use to Check if record exist in database?
thank’s before