MySQL - Update Column Value with Function and Trigger Before Insert - mysql

Question

i'm trying to update 2 column with trigger before insert, but i have unexpected result. i insert some data and the 2 last column will automatically inserted with values, here my first attempt
see? the last 2 column is null even i set some trigger and function to fill that columns automatically. Here my second attempt WITH EXACTLY SAME DATA
the last 2 column is filled with data, but i don't understand why the first attempt is fail?
here my trigger i use in the column total_harga
CREATE TRIGGER `set_total_harga` BEFORE INSERT ON `tbl_transaksi_detail`
FOR EACH ROW BEGIN
set NEW.total_harga = hitungTotalHargaPerItem(NEW.qty, NEW.harga_satuan);
END
trigger for column harga_satuan
CREATE TRIGGER `set_harga_satuan` BEFORE INSERT ON `tbl_transaksi_detail`
FOR EACH ROW BEGIN
set NEW.harga_satuan = set_Harga_Unit(NEW.unit, NEW.id_barang, NEW.no_transaksi);
END
function set_Harga_Unit
BEGIN
DECLARE
q,
id_toko INT;
SET
id_toko =(
SELECT DISTINCT
`tbl_transaksi`.`id_toko`
FROM
`tbl_transaksi`,
`tbl_transaksi_detail`
WHERE
`tbl_transaksi`.`no_transaksi` = no_trans
); IF unit = "PCS" THEN
SET
q =(
SELECT
`tbl_harga_jual`.`harga_pcs`
FROM
`tbl_harga_jual`
WHERE
`tbl_harga_jual`.`id_barang` = id_brg AND `tbl_harga_jual`.`id_toko` = id_toko
); RETURN q; ELSEIF unit = "PAK" THEN
SET
q =(
SELECT
`tbl_harga_jual`.`harga_pak`
FROM
`tbl_harga_jual`
WHERE
`tbl_harga_jual`.`id_barang` = id_brg AND `tbl_harga_jual`.`id_toko` = id_toko
); RETURN q; ELSEIF unit = "KARTON" THEN
SET
q =(
SELECT
`tbl_harga_jual`.`harga_karton`
FROM
`tbl_harga_jual`
WHERE
`tbl_harga_jual`.`id_barang` = id_brg AND `tbl_harga_jual`.`id_toko` = id_toko
); RETURN q;
END IF; RETURN q;
END
function hitungTotalHargaPerItem
BEGIN
DECLARE hasil int;
set hasil = qty * harga_satuan;
RETURN hasil;
END

Answer 1

The root cause serms to be the select that sets id_toko variable's value:
SET
id_toko =(
SELECT DISTINCT
`tbl_transaksi`.`id_toko`
FROM
`tbl_transaksi`,
`tbl_transaksi_detail`
WHERE
`tbl_transaksi`.`no_transaksi` = no_trans
);
In the select you inner join tbl_transaksi_detail (the table with the trigger in question) on another table. However, in the 1st case tbl_transaksi_detail is still empty (the trigger is before insert), therefore id_toko variable is set to null.
This will result q being null, which in turn results in the entire calculation set to null.
In the 2nd case there is already a record inserted into tbl_transaksi_detail table, therefore the calculation returns a non null value. But it returns the correct values only because the 1st and 2nd records' details are exactly the same.
I do not really understand that select that calculates id_toko anyway. If that is a transaction id, then you may use last_insert_id() if it is auto increment and the transaction record has just been created or max(id_toko) to get the highest value of id_toko (this is not multi user safe).

Answer 2

it seem i have mistaken select query in function set_Harga_Unit, based on clues from #Shadow
SET
id_toko =(
SELECT DISTINCT
`tbl_transaksi`.`id_toko`
FROM
`tbl_transaksi`,
`tbl_transaksi_detail`<<== I DON'T NEED THIS
WHERE
`tbl_transaksi`.`no_transaksi` = no_trans
); IF unit = "PCS" THEN
when first insert in tbl_transaksi_detail, the value no_transaksi is null because i use trigger before insert in empty table (tbl_transaksi_detail), so i remove tbl_transaksi_detail from query
SET
id_toko =(
SELECT DISTINCT
`tbl_transaksi`.`id_toko`
FROM
`tbl_transaksi`
WHERE
`tbl_transaksi`.`no_transaksi` = no_trans
); IF unit = "PCS" THEN
now it working, thanks everybody!