MYSQL stock entry - mysql

Question

PURCHASE TABLE
id (Primary Key) ItemNo, ItemName, Units, Qty, Location, CPrice,
SPrice, Supplier, PONo
STOCK TABLE
id (Primary Key), ItemNo, Qty, Location
IF EXISTS (SELECT ItemNo, Location FROM stock WHERE stock.ItemNo = 'poitem.ItemNo' AND stock.Location = 'poitem.Location') THEN
UPDATE stock SET stock.Qty = stock.Qty + poitem.Qty WHERE stock.ItemNo = 'poitem.ItemNo';
ELSE
INSERT INTO stock (stock.ItemNo, stock.Qty, stock.Location) SELECT poitem.ItemNo, poitem.Qty, poitem.Location FROM poitem;
END If
THis is my Code, but its not working as it should be
I need to update stock table when i enter a record through purchase table only is the record already exists, otherwise new record need to be entered.
Example:
ItemNo - Qty - Location
1001 - - - 15 - - - A
1001 - - - 12 - - - B
1002 - - - 50 - - - C
1003 - - - 12 - - - A
Can any one please write MYSQL code for this.
Thank you.

Answer 1

Your if exists will always evaluate to true (unless the stock table is empty) so the update will never happen (unless the stock table is empty). I think a procedure is inappropriate here unless you are calling it for every insert. Even if you are a trigger is probably a better bet.
drop trigger if exists t;
delimiter $$
create trigger t after insert on poitems
for each row
begin
IF EXISTS (SELECT ItemNo, Location FROM stock WHERE stock.ItemNo = new.ItemNo AND stock.Location = new.Location) THEN
UPDATE stock SET stock.Qty = stock.Qty + new.Qty WHERE stock.ItemNo = new.ItemNo and stock.Location = new.Location;
ELSE INSERT INTO stock (ItemNo, Qty, Location) values(new.ItemNo, new.Qty, new.Location) ;
END If;
end $$
I have also amended your update statement to match the if exists clause and fixed the insert statement and a few other things which looked wrong.
so given
drop table if exists poitems,stock;
create TABLE poitems(id int auto_increment Primary Key, ItemNo int, ItemName varchar(10), Units int, Qty int, Location int, CPrice int
, SPrice int, Supplier int, PONo int);
create table stock(id int auto_increment Primary Key ,ItemNo int, Qty int, Location int);
insert into poitems(itemno,qty,location) values (1,1,1),(1,1,1),(2,2,1);
results in
+----+--------+------+----------+
| id | ItemNo | Qty | Location |
+----+--------+------+----------+
| 1 | 1 | 2 | 1 |
| 2 | 2 | 2 | 1 |
+----+--------+------+----------+
2 rows in set (0.00 sec)