Procedure delete from different table - mysql

Question

I am trying to create a procedure that will delete everything related to the cust_id. When I enter the cust_id when I execute the procedure it deletes everything from the customer and invoice tables but not from the line table and I don't know why. This is what I have
BEGIN
DELETE FROM CUSTOMER WHERE CUS_CODE = cust_id;
DELETE FROM INVOICE WHERE INVOICE.CUS_CODE = cust_id;
DELETE FROM LINE WHERE EXISTS (SELECT * FROM INVOICE WHERE
INVOICE.INV_NUMBER = LINE.INV_NUMBER AND invoice.CUS_CODE = cust_id);
END

Answer 1

If you delete all records related to a customer from the invoices table first, then the exists() operator cannot return true for any of the records in the line table.
The easiest solution is to reverse the order of the deletion and delete from the line table first.
A slightly better solution is to use a multi-table delete syntax a delete the matching records from all 3 tables with a single statement:
delete invoice, customer, line
from customer
left join invoice on customer.cus_code=invoice.cus_code
left join line on invoice.inv_number=line.inv_number
where customer.cus_code=cust_id
But, the best would be to use foreign keys with the on delete cascade option set and do not use stored proc at all.
However, in most countries you are not allowed to delete invoices just like that, so you should really check your business requirements before implementing such deletion operation.