Question

如何根据其值返回一列或另一列？

我有以下存储过程（这只是一个示例）：

SELECT 
    Stds.FirstName, 
    Addrs.Address 
FROM
    Students AS Stds 
INNER JOIN 
    Address AS Addrs ON Addrs.StdId = Stds.StdId 
GROUP BY 
    Addrs.FirstName, 
    Stds.Address

现在的想法是Addresses有两个字段：Address和AddressTwo，我想返回AddressTwo IF {{1} }是Address的{{1}}。

Answer 1

好吧，对于我的特殊情况，也许通常我想使用ISNULL（）。

在此处回复： Select a column if other column is null

Answer 2

您可以使用COALESCE，例如：

SELECT 
    Stds.FirstName, 
    COALESCE(Addrs.Address, Addrs.AddressTwo) AS Addr
FROM 
    Students AS Stds INNER JOIN Address AS Addrs ON Addrs.StdId = Stds.StdId

Answer 3

您可以在下面的sql中使用。

SELECT 
    Stds.FirstName, 
    case when Addrs.Address is null then AddressTwo else  Addrs.Address end Address 
FROM
    Students AS Stds 
INNER JOIN 
    Address AS Addrs ON Addrs.StdId = Stds.StdId 
GROUP BY 
    Addrs.FirstName, 
    case when Addrs.Address is null then AddressTwo else  Addrs.Address end

SELECT子句中的IF

3 个答案: