UPDATE with set field determined conditionally not working? - mysql

Question

I have an after insert trigger on a table that is to update fields on another table based on the newly inserted row. (Its deducting stock qty in one location and adding to another location. Each column is a distict stock keeping location)
The exact field to be updated is determined from a select statment. Essentially
UPDATE stock SET FIELD1=FIELD1+NEW.stquantity, FIELD2=FIELD2-NEW.stquantity
WHERE FIELD1 and FIELD2 are determined by the case statement
The trigger I have looks like this now:
CREATE TRIGGER `changestockqty` AFTER INSERT ON `stocktransfer_items` FOR EACH ROW
BEGIN
DECLARE fromstocklocationvar INT DEFAULT -1;
DECLARE tostocklocationvar INT DEFAULT -1;
SET fromstocklocationvar = (SELECT stsource_location FROM stocktransfers WHERE stocktransfer.idstocktransfers=NEW.idstocktransfers);
SET tostocklocationvar = (SELECT stdest_location FROM stocktransfers WHERE stocktransfer.idstocktransfers=NEW.idstocktransfers);
UPDATE stock SET
CASE
WHEN fromstocklocationvar=1 THEN sl1
WHEN fromstocklocationvar=2 THEN sl2
WHEN fromstocklocationvar=3 THEN sl3
WHEN fromstocklocationvar=4 THEN sl4
WHEN fromstocklocationvar=5 THEN sl5
END
=
CASE
WHEN fromstocklocationvar=1 THEN sl1
WHEN fromstocklocationvar=2 THEN sl2
WHEN fromstocklocationvar=3 THEN sl3
WHEN fromstocklocationvar=4 THEN sl4
WHEN fromstocklocationvar=5 THEN sl5
END
-NEW.stquantity,
CASE
WHEN tostocklocationvar=1 THEN sl1
WHEN tostocklocationvar=2 THEN sl2
WHEN tostocklocationvar=3 THEN sl3
WHEN tostocklocationvar=4 THEN sl4
WHEN tostocklocationvar=5 THEN sl5
END
=
CASE
WHEN tostocklocationvar=1 THEN sl1
WHEN tostocklocationvar=2 THEN sl2
WHEN tostocklocationvar=3 THEN sl3
WHEN tostocklocationvar=4 THEN sl4
WHEN tostocklocationvar=5 THEN sl5
END
+NEW.stquantity,
WHERE stock.idstockpcode=NEW.stpcode;
END
It shows an error after the first case. What am I doing wrong?

Answer 1

Probably there is a syntax error (you try to use CASE statements to create another statement)..
Try this SQL (does the same thing):
CREATE TRIGGER `changestockqty` AFTER INSERT ON `stocktransfer_items` FOR EACH ROW
BEGIN
DECLARE fromstocklocationvar INT DEFAULT -1;
DECLARE tostocklocationvar INT DEFAULT -1;
SET fromstocklocationvar = (SELECT stsource_location FROM stocktransfers WHERE stocktransfer.idstocktransfers=NEW.idstocktransfers);
SET tostocklocationvar = (SELECT stdest_location FROM stocktransfers WHERE stocktransfer.idstocktransfers=NEW.idstocktransfers);
UPDATE stock SET
sl1 = CASE WHEN fromstocklocationvar=1 THEN sl1-NEW.stquantity ELSE sl1 END,
sl2 = CASE WHEN fromstocklocationvar=2 THEN sl2-NEW.stquantity ELSE sl2 END,
sl3 = CASE WHEN fromstocklocationvar=3 THEN sl3-NEW.stquantity ELSE sl3 END,
sl4 = CASE WHEN fromstocklocationvar=4 THEN sl4-NEW.stquantity ELSE sl4 END,
sl5 = CASE WHEN fromstocklocationvar=5 THEN sl5-NEW.stquantity ELSE sl5 END
,
sl1 = CASE WHEN tostocklocationvar=1 THEN sl1+NEW.stquantity ELSE sl1 END,
sl2 = CASE WHEN tostocklocationvar=2 THEN sl2+NEW.stquantity ELSE sl2 END,
sl3 = CASE WHEN tostocklocationvar=3 THEN sl3+NEW.stquantity ELSE sl3 END,
sl4 = CASE WHEN tostocklocationvar=4 THEN sl4+NEW.stquantity ELSE sl4 END,
sl5 = CASE WHEN tostocklocationvar=5 THEN sl5+NEW.stquantity ELSE sl5 END
WHERE stock.idstockpcode=NEW.stpcode;
END

Answer 2

You can't do it that way. The left side of Update have to be fixed.
Here is an example:
UPDATE stock SET
sl1=sl1 - CASE WHEN fromstocklocationvar=1 THEN NEW.stquantity ELSE 0 END
+ CASE WHEN tostocklocationvar=1 THEN NEW.stquantity ELSE 0 END,
sl2=sl2 - CASE WHEN fromstocklocationvar=2 THEN NEW.stquantity ELSE 0 END
+ CASE WHEN tostocklocationvar=2 THEN NEW.stquantity ELSE 0 END,
sl3=sl3 - CASE WHEN fromstocklocationvar=3 THEN NEW.stquantity ELSE 0 END
+ CASE WHEN tostocklocationvar=3 THEN NEW.stquantity ELSE 0 END,
sl4=sl4 - CASE WHEN fromstocklocationvar=4 THEN NEW.stquantity ELSE 0 END
+ CASE WHEN tostocklocationvar=4 THEN NEW.stquantity ELSE 0 END,
sl5=sl5 - CASE WHEN fromstocklocationvar=5 THEN NEW.stquantity ELSE 0 END
+ CASE WHEN tostocklocationvar=5 THEN NEW.stquantity ELSE 0 END
WHERE stock.idstockpcode=NEW.stpcode;