I'm using a trigger in order to make a Statistic Table. I have this many-to-many relationship where I have an Order that can have multiple Product's and viceversa. So after an INSERT on Order, using JPA, new rows are automatically inserted in the bridge table Order_Products.

When in the Trigger I use

    SET @numOfOPs = (
        SELECT COUNT(IDOrder) 
        FROM Order_Product 
        WHERE IDOrder = NEW.ID)

on new entries, the count on Order_Procut seems to return 0 (or the value before the insert on Order).

Here the signature of the Trigger:

    AFTER INSERT ON `Order` 

What could be the problem? I will add additional information if needed.

1 Answer 1


Don't you mean

( SELECT COUNT(*) FROM Order_Product
       WHERE ID_Order = NEW.ID_Order )

What will you be doing with @numOfOPs after the Trigger?

  • Well I tried both with and without IDOrder in the COUNT() but nothing changes. My need is to use @numOfOPs in an INSERT on a statistics table, in order the have directly the count without additional queries. May the problem be the fact that INSERT on Order happens before the INSERT on Order_Products? Commented Feb 13, 2022 at 15:12
  • @FilippoScaramuzza - My Answer focuses on NEW.ID_Order versus NEW.ID.
    – Rick James
    Commented Feb 13, 2022 at 20:08
  • Actually the field of the table Order is ID, not ID_Order. Commented Feb 13, 2022 at 21:49

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