Question

I need some help writing a MySQL trigger.
what i want to do is to calculated hashe value of autoincrement ID and store it in separate column:

create trigger hashing after insert on categories 
for each row begin
   set new.hashed = md5(CONCAT("key",`categories `.`id`));
end;

but i get error:

[Err] 1362 - Updating of NEW row is not allowed in after trigger

Can someone help me achieve what i need? Is this possible at all using triggers?

Thanks

Answer 1

What you are trying to do is not supported.

You can only set the value of the “hashed” column in a BEFORE INSERT trigger, not an AFTER INSERT trigger.

However, you can’t access the value of the auto-increment “id” column in a BEFORE INSERT trigger because that value is not known yet.

If you are determined to do this via a trigger, one option is to create a separate table to store the hashed value (along with a foreign key to reference the “categories” table), and insert into that table using an AFTER INSERT trigger on your “categories” table.