2 SQL中同一列的變量

Question

我很努力地理解下面的代碼段，因爲它涉及到整個腳本。有人能用簡單的英語向我解釋下面的代碼部分嗎？爲什麼有，看起來像一個'Seller_No'列的2個聲明變量？

SET @strSellerNo2 = NULL 

SELECT @strSellerNo2 = Seller_No 
FROM Outlet.tblProductMaster 
WHERE Product_No = @strProductNo 
     AND Seller_No <> @strSellerNo1 
     AND Product_Status = 'Available' 

---

USE [OutletRetail] 
GO 
/****** Object: StoredProcedure [Outlet].[sp_UpdateProductStatus] Script Date: 01/16/2014 19:58:47 ******/ 
SET ANSI_NULLS ON 
GO 
SET QUOTED_IDENTIFIER OFF 
GO 

--Updates Product status codes to Available if NULL 
ALTER PROCEDURE [Outlet].[sp_UpdateProductStatus] 
AS 

DECLARE @strProductNo varchar(20) 
DECLARE @strSellerNo1 varchar(10) 
DECLARE @strSellerNo2 varchar(10) 


DECLARE UpdateProductCursor CURSOR FOR 

    SELECT Product_No, Seller_No 
    FROM Outlet.tblProductMaster 
    WHERE Product_Status IS NULL 

OPEN UpdateProductCursor 
FETCH NEXT FROM UpdateProductCursor INTO @strProduct_No, @strSellerNo1 

WHILE @@FETCH_STATUS = 0 

BEGIN 

    SET @strSellerNo2 = NULL 

    SELECT @strSellerNo2 = Seller_No 
    FROM Outlet.tblProductMaster 
    WHERE Product_No = @strProductNo 
     AND Seller_No <> @strSellerNo1 
     AND Product_Status = 'Available' 


IF (@strSellerNo2 IS NULL) 
BEGIN 
     UPDATE Outlet.tblProductMaster 
     SET Product_Status = 'Available' 
     WHERE Product_No = @strProductNo 
      AND Seller_No = @strSellerNo1 
    END 


UPDATE Outlet.tblProductMaster 
SET Product_Status = 'Not Available' 
WHERE Product_No = @strProductNo 
     AND Seller_No <> @strSellerNo2 
     AND Product_Status IS NULL 

    FETCH NEXT FROM UpdateProductCursor INTO @strProductNo, @strSellerNo1 
END 

CLOSE UpdateProductCursor 
DEALLOCATE UpdateProductCursor 

Answer 1

希望這有助於;

SELECT @strSellerNo2 = Seller_No  -- Find me the Seller Number 
FROM Outlet.tblProductMaster   -- In the tblProductMaster table 
WHERE Product_No = @strProductNo  -- where the product number is the product we're looking for 
    AND Seller_No <> @strSellerNo1  -- and the Seller Number is not the Seller Number previously found 
    AND Product_Status = 'Available' -- and the Product Status is "Available"