尝试解决 MYSQL 更新触发器的语法错误

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 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$$