Can't Working my Before insert trigger in mysql - mysql

Question

I have created a before insert trigger when new value insert as it's item_sku already exits then delete already exit line and then insert new line. but it shows error:
Error Code: 1442
Can't update table 'order_item_temp' in stored function/trigger because it is already used by statement which invoked this stored function/trigger
Trigger Code is
TRIGGER LINE_DEL AFTER INSERT ON order_item_temp
FOR EACH ROW
BEGIN
DECLARE ITEM_D VARCHAR(50);
SELECT item_sku INTO #ITEM_D
FROM order_item_temp
GROUP BY item_sku,shopify_order_id
HAVING COUNT(item_sku) > 1;
DELETE FROM order_item_temp WHERE item_sku=#item_d;
END;
$$
DELIMITER ;
and by manual entry entering new duplicate line syntax is:
INSERT INTO ehad_db.order_item_temp (
id,
item_sku,
item_uid,
item_sid,
item_qty,
document_item_sid,
document_item_row_version,
ref_order_item_sid,
ref_order_item_row_version,
item_discount_amt,
item_discount_code,
item_discount_type,
item_discount_target,
shopify_order_id,
order_document_sid,
ref_order_sid
)
VALUES
(
'89',
'1000000009574',
'517662213000115019',
'32000000306430',
'1',
'582945547000174220',
'1',
' ',
' ',
'0',
' ',
' ',
' ',
'1903931129956',
'582945544000151211',
' ');
now it shows above error.

Answer 1

It seems you can't delete rows from order_item_temp in your trigger. According to the documentation:
A stored function or trigger cannot modify a table that is already
being used (for reading or writing) by the statement that invoked the
function or trigger.
Instead, you should handle it in your code using transaction like this
start_transaction();
delete_existed_rows();
insert_new_row();
commit();
or you could create a stored procedure that deletes already exited rows and inserts the new one, all in a transaction.
Here is an example code for creating a stored procedure
CREATE PROCEDURE insert_new_row(...)
BEGIN
DECLARE EXIT HANDLER FOR SQLEXCEPTION
BEGIN
ROLLBACK;
SIGNAL SQLSTATE 'ERROR'
SET MESSAGE_TEXT = 'INSERT FAILED';
END;
START TRANSACTION;
DECLARE ITEM_D VARCHAR(50);
SELECT item_sku INTO #ITEM_D
FROM order_item_temp
GROUP BY item_sku,shopify_order_id
HAVING COUNT(item_sku) > 1
FOR UPDATE;
DELETE FROM order_item_temp WHERE item_sku=#item_d;
INSERT INTO order_item_temp (...) VALUE (...);
COMMIT;
END;

Answer 2

You cannot put a trigger on order_item_temp that will SELECT/DELETE from the same table order_item_temp. Triggers cannot be used to update/delete the table that triggers them. Triggers should only be used to update other tables, not the one which is triggering the action.
What you are trying to do needs to be written in your coding language, so after you get a positive result for insert, you run the delete SQL.