"Condition expected" 尝试嵌套 CASE WHEN THEN 语句时出错

Question

我修改前的代码（运行良好）：

CASE WHEN b.EPIdentifier IS NOT NULL THEN b.EndTime

我在尝试实现一些进一步的嵌套 CASE WHEN THEN 逻辑时所做的更改：

CASE WHEN b.EPIdentifier IS NOT NULL THEN 
    CASE WHEN b.CancelEndTime IS NOT NULL THEN
        b.CancelEndTime
    ELSE CASE WHEN b.ExtendedEndDate IS NOT NULL THEN
        b.ExtendedEndDate
    ELSE CASE WHEN b.EndTime IS NOT NULL THEN
        b.EndTime
ELSE a.EndDate END EndDate

我在最后一个 EndDate:

上出错

an expression of non-boolean type specified in a context where a condition is expected

我不明白为什么会收到错误消息。我试着用 AS EndDate 代替，但我仍然遇到同样的错误。我把嵌套搞砸了吗？我什么也看不到。

Answer 1

您必须在每个 CASE WHEN 上放置一个 END。你的表情应该是这样的：

CASE WHEN b.EPIdentifier IS NOT NULL THEN 
    CASE WHEN b.CancelEndTime IS NOT NULL THEN b.CancelEndTime
    ELSE CASE WHEN b.ExtendedEndDate IS NOT NULL THEN b.ExtendedEndDate
         ELSE CASE WHEN b.EndTime IS NOT NULL THEN b.EndTime END
         END
    END
ELSE a.EndDate END EndDate

无论如何，您可以使用 COALESCE:

来简化表达式

CASE WHEN b.EPIdentifier IS NOT NULL THEN COALESCE(b.CancelEndTime, b.ExtendedEndDate, b.EndTime)
ELSE a.EndDate END EndDate

来自 MSDN:

The COALESCE expression is a syntactic shortcut for the CASE expression. That is, the code COALESCE(expression1,...n) is rewritten by the query optimizer as the following CASE expression:

CASE

   WHEN (expression1 IS NOT NULL) THEN expression1
   WHEN (expression2 IS NOT NULL) THEN expression2
   ...
   ELSE expressionN
END

Answer 2

END is the Part of CASE Statement, so you have to lookup for END.

CASE 语句的语法： SQL CASE

Simple CASE expression: 
CASE input_expression 
     WHEN when_expression THEN result_expression [ ...n ] 
     [ ELSE else_result_expression ] 
END 
Searched CASE expression:
CASE
     WHEN Boolean_expression THEN result_expression [ ...n ] 
     [ ELSE else_result_expression ] 
END

"Condition expected" 尝试嵌套 CASE WHEN THEN 语句时出错

"Condition expected" error when trying to nest CASE WHEN THEN statements

tsql

sql-server

case