SQL 服务器 - 添加条件内连接

Question

我是数据库开发的新手，我有一个存储过程，我需要在其中仅在满足条件时对表执行一些内部联接。以下是我的复杂查询的较短版本。

IF (testFunction(@UserId)) = 0 
  select C.AwardId, C.ProgramName, Count(ClientId) as Intakes from Client C 
    where C.Id = @ClientId
    group by C.AwardId, C.ProgramName...
ELSE
  select C.AwardId, C.ProgramName, Count(ClientId) as Intakes from Client C
    INNER JOIN UserRoleEntity URE ON C.AwardId = URE.EntityId 
    INNER JOIN UserRole UR ON URE.UserRoleId = UR.Id AND UR.CDPUserId = @UserId
         where C.Id = @ClientId
         group by C.AwardId, C.ProgramName...
END

基本上，它在 "IF" 和 "ELSE" 中都是相同的 SELECT 查询，只是在不满足 IF 条件时我需要对 2 个表进行内部联接。不是在 "IF" 和 "ELSE" 中重复查询，有没有办法让它成为一个单一的查询而不去动态查询？

谢谢！

Answer 1

如果我的查询正确，您想要显示所有字段，即使 CDPUserID 不存在或 0 对吗？您只需要 FULL JOIN 在第二个连接中：

SELECT C.AwardId, C.ProgramName, Count(ClientId) as Intakes FROM Client C
INNER JOIN UserRoleEntity URE ON C.AwardId = URE.EntityId 
FULL JOIN UserRole UR ON URE.UserRoleId = UR.Id AND UR.CDPUserId = @UserId
     WHERE C.Id = @ClientId
     GROUP BY C.AwardId, C.ProgramName...

Answer 2

在 where 条件中使用 OR 和 EXISTS()

select C.AwardId, C.ProgramName, Count(ClientId) as Intakes from Client C
where 
    (testFunction(@UserId)) = 0 
    OR 
    (
      EXISTS
      (
        SELECT * FROM UserRoleEntity URE INNER JOIN UserRole UR ON URE.UserRoleId = UR.Id AND UR.CDPUserId = @UserId
        WHERE C.AwardId = URE.EntityId 
      ) 
      AND C.Id = @ClientId
    )
group by C.AwardId, C.ProgramName...

Answer 3

您可以使用额外的 WHERE 条件和 LEFT JOIN 进行条件过滤：

SELECT C.AwardId, C.ProgramName, Count(ClientId) as Intakes 
FROM Client C
LEFT JOIN UserRoleEntity URE ON C.AwardId = URE.EntityId 
LEFT JOIN UserRole UR ON URE.UserRoleId = UR.Id AND UR.CDPUserId = @UserId
WHERE C.Id = @ClientId
 AND (   testFunction(@UserId) = 0
      OR (testFunction(@UserId) <> 0 AND URE.AwardID IS NOT NULL AND UR.ID IS NOT NULL))
GROUP BY C.AwardId, C.ProgramName

SQL 服务器 - 添加条件内连接

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