当列不存在时，为什么 IF EXIST 不跳过第一个代码块？

Question

我正在尝试在多个数据库中运行一段代码。一列 Mfg_ID 存在于某些表中，但不存在于其他表中。我尝试了 IF EXISTS 语句。当该列不存在时，它会抛出一个错误，就好像它运行了应该跳过的块一样。 （列名称“Mfg_ID”无效。）

显然，SQL 会检查代码是否有效，即使它跳过了那段代码？我该如何解决这个问题？下面的代码....

IF EXISTS(SELECT 1 FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 'Inv_Dtl_3834' AND COLUMN_NAME = 'Mfg_ID')

BEGIN
    BEGIN TRY
        SELECT  CAST(SUBSTRING(SUBSTRING(DB_NAME(), 3, 255), 1, 
                CHARINDEX('_', SUBSTRING(DB_NAME() , 3, 255))-1) AS INT) AS 
                       CID, 
                SUBSTRING(SUBSTRING(DB_NAME(), 3, 255), CHARINDEX('_', 
                SUBSTRING(DB_NAME() , 3, 255))+1, 255) AS Client,
                Vend_Num, 
                Vend_Name, 
                Min(InvDate) AS Min_InvDate, 
                MAX(InvDate) AS Max_InvDate, 
                Item_Num, 
                VITEM_Num, 
                Mfg_ID,
                Item_Desc, 
                SUM(InvQty) AS InvQty, 
                InvPrice
        FROM Inv_Dtl_3834
        GROUP BY Vend_Num, Vend_Name, Item_Num, VITEM_Num, Mfg_ID, Item_Desc, InvPrice
    END TRY

    BEGIN CATCH

    END CATCH
END
ELSE
BEGIN
    SELECT  CAST(SUBSTRING(SUBSTRING(DB_NAME(), 3, 255), 1, CHARINDEX('_', 
            SUBSTRING(DB_NAME() , 3, 255))-1) AS INT) AS CID, 
            SUBSTRING(SUBSTRING(DB_NAME(), 3, 255), CHARINDEX('_', 
            SUBSTRING(DB_NAME() , 3, 255))+1, 255) AS Client,
            Vend_Num, 
            Vend_Name, 
            Min(InvDate) AS Min_InvDate, 
            MAX(InvDate) AS Max_InvDate, 
            Item_Num, 
            VITEM_Num, 
            'N/A' AS Mfg_ID,
            Item_Desc, 
            SUM(InvQty) AS InvQty, 
            InvPrice
    FROM Inv_Dtl_3834
    GROUP BY Vend_Num, Vend_Name, Item_Num, vITEM_Num, Item_Desc, InvPrice
END

我在有和没有 BEGIN TRY 部分的情况下都运行过这个。我已经删除了代码并将其替换为虚拟代码，例如 SELECT 'The field does not exist' 并且有效。