T-SQL中的嵌套If条件

Question

Hello i have the following store procedure:

    CREATE PROCEDURE update_stock_level
(
    @ItemID int,
    @Quantity int = 1,
    @Return int = 0
)
AS

    IF @Return = 0
        UPDATE  Stock
        SET     Quantity    = (Quantity - @Quantity)
        WHERE   ItemID      =   @ItemID

    ELSE 
        UPDATE  Stock
        SET     Quantity    = (Quantity + @Quantity)
        WHERE   ItemID      =   @ItemID

This stored procedure is for A POS application, what this procedure does(should do) is update(increase or decrease) the stock level based on the item id and the item's quantity.

ItemID -> ID of item selected from front end. Quantity -> How many items Return -> If return is '0' that means it is false, meaning this is not a return sale if it is '1' it means an item is being returned in which case the stock should increase by the quantity returned. If nothing is passed to the qantity parameter then the default is 1.

My issue now is that the stock level get's reduced fine but it does not increase when a return is made.

Answer 1

Leave just ELSE part:

IF @Return = 0
    UPDATE  Stock
    SET     Quantity    = (Quantity - @Quantity)
    WHERE   ItemID      =   @ItemID
ELSE 
    UPDATE  Stock
    SET     Quantity    = (Quantity + @Quantity)
    WHERE   ItemID      =   @ItemID

Alternatively you can do it in a single statemnet:

UPDATE  Stock
SET     Quantity    = Quantity - @Quantity * POWER(-1,@Return)
WHERE   ItemID      = @ItemID

If @Return=0 then power(-1,0) = 1 and you decrease stock.

If @Return=1 then power(-1,1) = -1 and you increase stock.