Question

I have a very simple question, so I hope someone will help.

I have a MySQL table with ID and CREDIT. I want to do an update trigger, which would change the update value if credit is 0. So something like “if old.CREDIT = 0 then new.CREDIT = 0.001”. So what will be the syntax of the trigger? Thanks.

Answer 1

Please read tutorial on MySQL Triggers which gives simple to complex examples.
Here is a simple example on before update trigger, that may help you.

Assuming table name as credit_info.

delimiter //
create trigger sample_trigger_before_update_on_credit_info before update on test.credit_info
  for each row begin
    if new.credit = 0 then
      set new.credit = 0.001;
    end if;
  end;
//
delimiter ;

Let us say, table have 2 records as follows:

+------+--------+
| id   | credit |
+------+--------+
|    1 |  1.000 |
|    2 |  3.000 |
+------+--------+

When you issue an update statement as:

update credit_info set credit=0 where id=2;

The resulting record would be as follows:

+------+--------+
| id   | credit |
+------+--------+
|    2 |  0.001 |
+------+--------+

Let me hope, sample example will accelerate your energies.