Trying to resolve a syntax error for MYSQL update trigger - mysql

Question

I am trying to create a trigger to update the Project table whenever the Assign table is updated, yet I keep receiving this error: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'END IF
Does anyone have any idea of why I am getting this syntax error? Please note that I am a beginner at this so my SQL statements may be entirely wrong. Also, I know for sure that my query being ran in my IF statement works because I've ran it on its own without being inside a trigger.
delimiter $$
CREATE TRIGGER update_trigger AFTER UPDATE ON Assign
FOR EACH ROW
BEGIN
IF OLD.projNo <> new.projNo THEN
#RUN THIS QUERY TO UPDATE MY TABLE
UPDATE Project p JOIN
(SELECT Project.projNo, COUNT(DISTINCT empid) as numEmployeeAssigned
FROM (Project LEFT JOIN Assign ON Project.projNo=Assign.projNo)
GROUP BY projNo
) as tb
ON p.projNo = tb.projNo
SET p.numEmployeeAssigned = tb.numEmployeeAssigned
#END QUERY
END IF
END$$
delimiter;

Answer 1

You can just increment or decrement the count:
UPDATE Project p
SET p.numEmployeeAssigned = p.numEmployeeAssigned +
(case when p.projNo = new.ProjNo then 1 else -1 end)
WHERE p.projNo IN (old.ProjNo, new.ProjNo) AND
old.ProjNo <> new.ProjNo;

Answer 2

Obviously, your code is missing semi-colons after the UPDATE statement and after the END IF.
However, let me suggest that the UPDATE statement could most likely be simplified. As I understand your code, you want to update the count of employees in Project whenever an employee changes its assignment. If so, there is no need to actually query assign. You can just use conditional logic like this:
CREATE TRIGGER update_trigger AFTER UPDATE ON Assign
FOR EACH ROW
BEGIN
IF OLD.projNo <> new.projNo THEN
UPDATE Project p
SET numEmployeeAssigned = CASE
WHEN projNo = new.projNo THEN numEmployeeAssigned + 1
ELSE numEmployeeAssigned - 1
END
WHERE projNo IN (OLD.projNo, NEW.projNo);
END IF;
END$$
You could even remove the IF statement and put that condition in the query directly:
CREATE TRIGGER update_trigger AFTER UPDATE ON Assign
FOR EACH ROW
BEGIN
UPDATE Project p
SET numEmployeeAssigned = CASE
WHEN projNo = new.projNo THEN numEmployeeAssigned + 1
ELSE numEmployeeAssigned - 1
END
WHERE projNo IN (OLD.projNo, NEW.projNo) AND OLD.projNo <> NEW.projNo
END$$