Question

我有一个带有case子句的简单变量分配，例如：

DECLARE @CurrentType INT

SELECT
     @CurrentType = (CASE
                     WHEN [CL].[ProjectKey] IS NOT NULL
                     THEN 0
                     ELSE 1
                  END)
     FROM [Project] AS [P]
         LEFT JOIN [CallLog] AS [CL] ON [P].[ProjectKey] = [CL].[ProjectKey]


SELECT
     @CurrentType

但是它总是返回NULL而不是1或0

我也尝试使用IIF有条件的条件，例如：

DECLARE @CurrentType INT = (SELECT 
                            IIF([CL].[ProjectKey] IS NOT NULL , 1 , 0)
                            FROM [Project] AS [P]
                                LEFT JOIN [CallLog] AS [CL] ON [P].[ProjectKey] = [CL].[ProjectKey] )

                                SELECT
                 @CurrentType

但是，同样的历史，我怎样才能得到欲望的结果？是1还是0？问候

Answer 1

此表达式：

SELECT @CurrentType = (CASE WHEN [CL].[ProjectKey] IS NOT NULL THEN 0 ELSE 1 END)
FROM [Project] [P] LEFT JOIN
     [CallLog] [CL]
      ON [P].[ProjectKey] = [CL].[ProjectKey];

如果查询未返回任何行，则只能将@CurrentType设置为NULL。假设您使用的是LEFT JOIN，则意味着Project为空。

如果将其更改为聚合查询，还将获得一行，因此这可能会满足您的要求：

SELECT @CurrentType = (CASE WHEN MAX([CL].[ProjectKey]) IS NOT NULL THEN 0 ELSE 1 END)
FROM [Project] [P] LEFT JOIN
     [CallLog] [CL]
      ON [P].[ProjectKey] = [CL].[ProjectKey];

根据条件设置变量

1 个答案: