使用触发器来实现引用完整性操作（SQL Server）

Question

I'm trying to implement some triggers for my tables

2 of the tables are ORDERS (has orders) and ORDERS_ITEMS (has items for each order), and I want to delete the ORDER when there are no more ITEMS in that ORDER .

I want my trigger to look something like this

CREATE TRIGGER DELETE_ORDER_WHEN_NO_ITEMS
INSTEAD OF DELETE 
ON ORDER
    DECLARE rowcount int;
BEGIN
    // First detemine if this is the last item in the ORDER
    SELECT Count(*) 
    INTO rowcount 
    FROM ORDER_ITEM 
    WHERE ORDER_ITEM.ItemNumber = old:ItemNumber;

    // Delete ITEM row
    DELETE ORDER_ITEM 
    WHERE ORDER_ITEM.ItemNumber = old:ItemNumber;

    // Last ITEM in ORDER delete the whole ORDER 
    IF (rowcount = 1) THEN
       DELETE ORDER 
       WHERE ORDER.OrderNumber = old:OrderNumber;
    END IF
END;

I'm not sure how to write this in SQL Server and I had the algorithm from a book but I couldn't run it on SQL Server.

Answer 1

Don't use a trigger for that. Use foriegn key with cascade delete.

Update

Sorry, I've jumped to the wrong conclution. If you want to delete the orders when there are no items connected to it, cascade delete will not help.
Use a triger for after delete on the order_item table and write this delete statement there: ( updated again )

CREATE TRIGGER order_item_delete ON order_item
FOR DELETE
AS 

DELETE order
FROM order
INNER JOIN deleted ON (order.OrderNumber = deleted.OrderNumber) -- 1
LEFT JOIN order_Item ON(order.OrderNumber = order_item.OrderNumber) 
WHERE order_Item.ItemNumber IS NULL -- 2

GO

Breakdown:

1. The inner join with deleted table will ensures you only delete records where the OrderNumber is the same as the deleted records from order_item table.
2. The left join with order_item table along with the where clause ensures you only delete records from orders table if they have no order_item records attached to them.

Answer 2

Your syntax looks more like Oracle; SQL Server syntax is quite different. For instance, there is no new: and old: . Instead, there are tables, inserted and deleted .

If I understand correctly, you want to remove one item from the orders in the delete statement. Then, if the last item has been removed, you want to delete the order itself. I think the following does this:

CREATE TRIGGER trg_orders_delete_one_item ON orders
    INSTEAD OF DELETE    
AS
begin
    with todelete  as (
        select oi.*, row_number() over (partition by OrderId order by ItemNumber desc) as seqnum
        from Order_Items oi
        where oi.OrderId in (select OrderId from deleted)
    )
    delete todelete
        where seqnum = 1;

    with todelete as (
          select o.*
          from orders o
          where o.OrderId in (select OrderId from deleted)
         )
    delete todelete
        where not exists (select 1
                          from order_item oi
                          where oi.OrderId = todelete.OrderId
                         )
end;