Prevent having a zero value in a mysql field

Question

I have a table like this:

CREATE TABLE mytable (   
  id int(10) unsigned NOT NULL AUTO_INCREMENT,   
  mynum int(10) unsigned NOT NULL,  
)

The default value for an int is 0 (zero). In my application, 0 is an invalid value for "mynum".

How can I ensure that a 0 is never entered for mynum? I can do the check in my application code, but I wish I didn't have to do that. I want mysql to prevent any insert of value 0 in the mynum field.

Thanks.

Answer 1

You can do this in MySQL 5.5 with the SIGNAL syntax in a TRIGGER.

Source: http://dev.mysql.com/doc/refman/5.5/en/signal.html

You can do it then with the following TRIGGER:

create trigger mytable_zero_check
before insert on my_table
for each row
begin
    if(new.mynum = 0) then
        SIGNAL 'your error message'
    end if 
end

If you are running < 5.5, then you can make a syntax error (for example assigning NULL to a field that does not allow NULLs), and the INSERT will be aborted aswell.