cannot delete row from database using php - php

Question

I am unable to delete any record from database. I cannot find any error in this.
I have deleted records from another table by just changing a little bit but here it's not working. Below is the code to apply the delete query.The name of table is from where I want to delete records but its not happening here.
deleteSupplier.php
<?php
mysql_connect("localhost","root","");
mysql_select_db("db_kiln");
$id1 = $_GET['id1'];
$query0 = "DELETE FROM tbl_supplier WHERE sup_id='$id1'";
if(mysql_query($query0)){
echo "<script>window.open('supplier_connect.php','_self')</script>";
}
else{
echo "Not deleted";
}
?>
This is the file where I fetch data from database and have delete button against each record. When I click on the button it does not delete record and show the error message. I can't find any error I think there is a logical error in this code. Please help.
supplier_connect.php
<?php
mysql_connect("localhost","root","");
mysql_select_db("db_kiln");
$query = "Select * from tbl_supplier";
$run = mysql_query($query);
echo "<table border='1'>
<tr>
<th>Supplier Id</th>
<th>Name</th>
<th>Contact Number</th>
<th>Quotation </th>
<th>Remove</th>
</tr>";
while($row = mysql_fetch_assoc($run)){
echo "<tr>";
echo "<td>" . $row['sup_id'] . "</td>";
echo "<td>" . $row['sup_name'] . "</td>";
echo "<td>" . $row['sup_contact'] . "</td>";
echo "<td>" .$row['sup_quotation']. "</th>";
echo '<td>Delete</td>';
echo "</tr>";
}
echo "</table>";
?>

Answer 1

You probably have the ID of the supplier referencing to another table, and upon DELETE, no action is set. You need to set the option 'upon DELETE: Cascade or SET NULL.' I'd go for SET NULL, else your whole reference record will be deleted as well.
EDIT: check the relationship between your contacts and quotations, see where your supplierid is going to.