Syntax error in my trigger

[Ilyass G]

Hello,

I am currently trying to create a trigger that assigns a code (PK) to inserted rows. Since I need this for a Java program, I was thinking about inserting rows where code is 0 and then using the trigger to give them a unique value.

e.g: INSERT INTO S values(0);

Unfortunately, my tries have been unsuccessful so far, as I either get a syntax error or an "unknown system variable 'code'". Here is what I have done so far:

CREATE TRIGGER codeset BEFORE INSERT ON S FOR EACH ROW
BEGIN
     SET @max = (SELECT MAX(code) FROM S);
     SET code = 1 + @max;
END;

Thank you for your help,