IF EXISTS 语句中的 UNION 不起作用 [英] UNION inside IF EXISTS statement not working

问题描述

SELECT A, B, C FROM TUser

UNION

IF EXISTS(SELECT dataUserId FROM TUserData WHERE DataId = @dataId AND UserId = @userId)
  BEGIN
    SELECT @dataUserId  = dataUserId FROM TUserData WHERE DataId = @dataId AND UserId = @userId

    SELECT A, B, C FROM TUser WHERE UserId = dataUserId 
  END

推荐答案

你可以这样转换:

SELECT @dataUserId  = dataUserId FROM TUserData
WHERE DataId = @dataId AND UserId = @userId

IF (@dataUserId IS NOT NULL)
  BEGIN
    SELECT A, B, C FROM TUser
    UNION
    SELECT A, B, C FROM TUser WHERE UserId = @dataUserId 
  END
ELSE
  SELECT A, B, C FROM TUser

这篇关于IF EXISTS 语句中的 UNION 不起作用的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！