案例表达只显示一次

Question

我有一个案例表达，我有困难：

WHEN @CustomerID = 3 AND @OrderID = 2 AND @Name IN ('Hello') THEN 'Regular'
WHEN @CustomerID = 3 AND @OrderID = 2 AND @Telephone = 1 AND @Name IN ('Hello') THEN 'Business'

如果我有两个语句，它只返回'Regular'，但如果我取出'Regular'，它会显示Business。我究竟做错了什么？

Answer 1

如果你想要其中一个或两个，那么它需要是两个单独的列，或者如果你想要一个列包含两个输出：

或者：

case WHEN @CustomerID = 3 AND @OrderID = 2 AND @Name IN ('Hello') THEN 'Regular' end,
case WHEN @CustomerID = 3 AND @OrderID = 2 AND @Telephone = 1 AND @Name IN ('Hello') THEN 'Business' end

要么：

WHEN @CustomerID = 3 AND @OrderID = 2 AND @Telephone = 1 AND @Name IN ('Hello') THEN 'Regular, Business' 
WHEN @CustomerID = 3 AND @OrderID = 2 AND @Name IN ('Hello') THEN 'Regular'

Answer 2

返回的值将是匹配的最早WHEN子句（文本）的THEN表达式的值。

在您的查询中，Second WHEN子句包含First WHEN子句的一部分。这意味着，只要第二个为真，第一个WHEN条款就会成立。然后返回那个表达式（第一个）WHEN条款。

查询-1：

SELECT CASE WHEN @CustomerID = 3 AND @OrderID = 2 AND @Name IN ('Hello') THEN 'Regular'
WHEN @CustomerID = 3 AND @OrderID = 2 AND @Telephone = 1 AND @Name IN ('Hello') THEN 'Business' END

查询-2：

SELECT CASE WHEN @CustomerID = 3 AND @OrderID = 2 AND @Telephone = 1 AND @Name IN ('Hello') THEN 'Business'
WHEN @CustomerID = 3 AND @OrderID = 2  AND @Name IN ('Hello') THEN 'Regular' END

输入：

@CustomerID INT=3
@OrderID INT = 2
@Name VARCHAR(100)='Hello'
@Telephone INT=1

输出：

Query1 : 'Regular'
Query1 : 'Business'

输入：

@CustomerID INT=3
@OrderID INT = 2
@Name VARCHAR(100)='Hello'
@Telephone INT=0

输出：

Query1 : 'Regular'
Query1 : 'Regular'