Create Trigger MySql update or insert in another table

I am trying to learn more about triggers in mysql, so bear with me. I have two tables,

TestTable  
 (id INTEGER PRIMARY KEY AUTO_INCREMENT, ItemId INTEGER,Date date, Value REAL)

TestTable2
 (id INTEGER PRIMARY KEY AUTO_INCREMENT, ItemId INTEGER,Year INTEGER, Month INTEGER, Open REAL, Close REAL, Increase REAL)

Where the table TestTable is measurements on a certain item on a specific date. TestTable2 contains measurements for a specific month,year and the increase during this period.

I want to create a trigger which updates or insert values into TestTable2 as I insert values into TestTable.

This is what the trigger i tried to create looked like,

CREATE TRIGGER 'monthUpdateTrigger' AFTER INSERT ON TestTable 
BEGIN 
IF NOT (EXISTS (SELECT 1 FROM TestTable2 WHERE 
(ItemId=NEW.ItemId AND Year=YEAR(NEW.Date) AND Month=MONTH(NEW.Date)))) 
THEN 
    INSERT INTO TestTable2 (ItemId,Year,Month,Open,Close,Increase ) VALUES 
    (NEW.ItemId , YEAR(NEW.Date), MONTH(NEW.Date),NEW.Value,NEW.Close,0.0); 
ELSE
    UPDATE TestTable2 SET Close=NEW.Close AND Increase=(NEW.Close/(SELECT 
    Open FROM TestTable WHERE (Year=YEAR(NEW.Date) and Month=MONTH(NEW.Date))) 
    WHERE (Year=YEAR(NEW.Date) and Month=MONTH(NEW.Date))
END IF;
END;

But this does not seem to work, I get the error,


You have an error in your SQL syntax; check the manual that
corresponds to your MySQL server version for the right syntax to use
near 'BEGIN IF NOT (EXISTS (SELECT 1 FROM TestTable WHERE
(ItemId=NEW.ItemId AND Yea' at line 1

Can someone please point out the error/errors. Or offer a better solution to this problem.

First, you need to specified when do you want to run the trigger inside the table. I've edited your trigger and use AFTER UPDATE and AFTER INSERT:

AFTER INSERT:

USE `TEST`;
DELIMITER $
DROP TRIGGER IF EXISTS MEDICAMENTO.monthUpdateTriggerAI$
USE `TEST`$
    CREATE DEFINER = CURRENT_USER TRIGGER `TEST`.`monthUpdateTriggerAI` AFTER INSERT ON `TestTable` FOR EACH ROW
    BEGIN
    SET @COUNT=(SELECT COUNT(*) FROM TestTable2 WHERE (ItemId=NEW.ItemId AND Year=YEAR(NEW.Date) AND Month=MONTH(NEW.Date)));
    IF @COUNT=0 THEN
        INSERT INTO TestTable2 (ItemId,Year,Month,Open,Close,Increase ) VALUES 
        (NEW.ItemId , YEAR(NEW.Date), MONTH(NEW.Date),NEW.Value,NEW.Close,0.0); 
    ELSE
        UPDATE TestTable2 SET TestTable2.Close=NEW.Close AND Increase=(NEW.Close/(SELECT 
        Open FROM TestTable WHERE (Year=YEAR(NEW.Date) and Month=MONTH(NEW.Date)) LIMIT 1))
        WHERE (Year=YEAR(NEW.Date) and Month=MONTH(NEW.Date));
    END IF;
    END;
$
DELIMITER ;

AFTER UPDATE:

USE `TEST`;
DELIMITER $
DROP TRIGGER IF EXISTS MEDICAMENTO.monthUpdateTriggerAU$
USE `TEST`$
    CREATE DEFINER = CURRENT_USER TRIGGER `TEST`.`monthUpdateTriggerAU` AFTER UPDATE ON `TestTable` FOR EACH ROW
BEGIN

    UPDATE TestTable2 SET TestTable2.Close=NEW.Close AND Increase=(NEW.Close/(SELECT 
    Open FROM TestTable WHERE (Year=YEAR(NEW.Date) and Month=MONTH(NEW.Date)) LIMIT 1))
    WHERE (Year=YEAR(NEW.Date) and Month=MONTH(NEW.Date));

END;
$
DELIMITER ;

Note: Be careful about the SELECT Open FROM TestTable WHERE (Year=YEAR(NEW.Date) and Month=MONTH(NEW.Date)), I've added a LIMIT 1 to avoid duplicate rows.

Change the database TEST.

You can also use ON DUPLICATE KEY on the two triggers execution.

You can get more information in the MySQL's documentation manual.

StackExchange Database Administrators Q#115632, answer score: 2