SQL根據庫存和交易計算餘額

Question

我正在創建一個用於計算用戶庫存狀態的存儲過程。

設想以下的表稱爲user_inventory許多偶數列：

id_inventory id_user 0 1 2 3 
------------ ------- - - - - 
      2   4 5 0 14 21 

而另一位叫user_transactions

id_tran id_user 0 1 2 3 
------- ------- - - - - 
    54   4 1 0 3 7 
    55   4 2 0 9 8 
    56   4 1 0 2 4 

我想是計算每一列的剩餘庫存狀態的方法減去所有用戶交易的總和後，如下所示：

id_availableInventory id_user 0 1 2 3 
--------------------- ------- - - - - 
        2   4 1 0 0 2 

附加障礙是，有從0標記的列499。

我試圖使用while循環和使用動態SQL和SUM（）在更新一次一列，但有兩個範圍和性能問題 - 我不確定這是否是解決此問題的好方法。我使用SQL Server 2012的

DECLARE @counter int 
DECLARE @userid int 
DECLARE @amount int 
DECLARE @sum int 
declare @sql nvarchar(1000) 
SET @counter = 0 
SET @userid = 4 
WHILE @counter < 500 
BEGIN 
    set @sql = 'SELECT @amount = [' + CAST(@counter AS nvarchar) + '] FROM user_inventory WHERE ID_User = ' +CAST(@userid AS nvarchar) 
    EXEC(@sql) 
    set @sql = 'SELECT @sum = SUM([' + CAST(@counter AS nvarchar) + ']) FROM user_transactions WHERE ID_User = ' +CAST(@userid AS nvarchar) 
    EXEC(@sql) 
    set @sql = 'UPDATE user_availableinventory SET [' + CAST(@counter AS nvarchar) + '] = @amount - @sum WHERE ID_User = ' +CAST(@userid AS nvarchar) 
    EXEC(@sql) 
    SET @counter = @counter + 1 
END 

這回Must declare the scalar variable "@amount".多次。 我知道這是一個醜陋的方法，對此問題的任何建議都非常感激。

Answer 1

您正在接收錯誤，因爲您正在使用變量範圍之外的變量。查詢字符串作爲單獨的會話執行，因此您需要在查詢字符串中聲明變量。

可以通過聲明的查詢字符串

DECLARE @counter int 
DECLARE @userid int 
declare @sql nvarchar(1000) 
SET @counter = 0 
SET @userid = 4 
WHILE @counter < 500 
BEGIN 
    set @sql = ' 
    DECLARE @sum int 
    DECLARE @amount int 

    SELECT 
     @amount = [' + CAST(@counter AS nvarchar) + '] 
     FROM user_inventory WHERE ID_User = ' +CAST(@userid AS nvarchar)+' 

    SELECT 
     @sum = SUM([' + CAST(@counter AS nvarchar) + ']) 
     FROM user_transactions WHERE ID_User = ' +CAST(@userid AS nvarchar)+' 

    UPDATE user_availableinventory SET [' + CAST(@counter AS nvarchar) + '] = @amount - @sum WHERE ID_User = ' +CAST(@userid AS nvarchar) 

    EXEC(@sql) 
    SET @counter = @counter + 1 

END