How to compare two tables mysql? - php

Question

I have three tables :
Table 1 is called "card" . The fields that are important are:
"state_id" - This table has 3 values (1,2,3)
"associated_driver" - called "referred_as" on driver table
"referred_as" - called "associated_card" on driver table
Table 2 is called "driver". The fields that are important are:
"ID" - The auto incremented value of the table
"associated_card" - Has a value , normally some number e.g 123555
"referred_as" - The name of the driver () called "associated_driver" on card table
Forgot to add this table :
Table 3is called "card_driver". The fields that are important are:
"driver_id" - The id from the driver table that links to the card
"card_id" - The id from the card table that links to the driver
What i want to happen :
When a user enters their id from the driver table, it will compare a field that both tables have i.e the 'associated card' field. From there the original query from (bellow) will take over, although that needs to be modified as well.
I don't really know how to do sql queries .
I need to change this part :
$sql ="SELECT * FROM card WHERE id = '$id'" ;
Thanks
Original Code :
$id = $_POST['id'];
$sql ="SELECT * FROM card WHERE id = '$id'" ;
mysql_select_db('damp');
$result = mysql_query( $sql, $conn );
$row = mysql_fetch_assoc($result);
switch($row['state_id'])
{
case "1":
echo "<strong><font color=\"green\">Authorisation Granted!</font></strong>";
break;
case "2":
echo "<strong><font color=\"red\">Your card has expired and authorisation is denied</font></strong>";
break;
case "3":
echo "<strong><font color=\"red\">Your card has been cancelled and authorisation is denied</font></strong>";
break;
default:
echo "<strong><font color=\"red\">The Card ID does not exist</font></strong>";
}
//echo $_GET['here']; // Prints the name of the page content
//echo $class_obj_id; // Prints the id number of the selected row
?>
<?php } ?>
<div id="auth">
<form method="post" action="<?php $_PHP_SELF ?>">
<table id="auth" width="150" >
<tr>
<td colspan="2"><h2>Check Card Authorisation</h2></td>
</tr>
<tr>
<td width="50" align="center">ID</td>
<td><input name="id" type="text" id="id" value="" /></td>
</tr>
<tr>
<td width="100"> </td>
<td>
<input name="check" type="submit" id="check" value="Check">
</td>
</tr>
</table>
</form>
</div>

Answer 1

$sql ="SELECT * FROM card c JOIN driver d ON c.referred_as=d.referred_as WHERE d.ID='$id'";

Answer 2

$sql = "SELECT * FROM driver INNER JOIN card ON driver.associated_card = card.associated_card WHERE id = '$id'";
Join the driver and card tables where the associated card id matches up, then you can just call your $row['state_id'] from this