Comments - Trigger keeps creating error

Delimiters show the client program (HeidiSQL in your case) where a query ends, and the client sends the entire chunk of SQL to the server as a single query. The default delimiter is semicolon. So, in your initial example, the client sends everything from CREATE and up and including SET NEW.ClGender ='U', which of course does not make a complete valid query. This is what the server complains about in the error message -- it finds emptiness where it expects something else.

When you change the delimiter and use it at the end of the trigger definition, the client understands that the whole definition should be sent as a whole, and the server is able to interpret it correctly.

It is perfectly fine to use non-default delimiters when you define stored procedures (including triggers); you don't need to invent tricks to avoid it. It is not always possible anyway.

But if you are curious, in your case you could phrase it like this:

CREATE TRIGGER trig_client_gndr 
BEFORE INSERT ON WM_CLIENT 
FOR EACH ROW 
SET NEW.ClGender = IF(NEW.ClGender NOT IN ('M','F'),'U',NEW.ClGender);

I think it should have worked.

Thank you for that follow up. Now that all makes sense. I have been using Oracle for school, but I am now using MariaDB at home.

The two RDBMS have enough differences to be frustrating when migrating.

Again, thanks.