Question

嘿聪明人。我遇到以下SQL语句的问题。我知道我不能在OnlineStatus列上做GROUP BY，这是有意义的，因为它是一个函数调用，而不是我表中的实际列。我如何修改这个以便我可以计算有多少用户在线？

SELECT CASE dbo.fnGetWebUserOnlineStatus(W.Id) 
        WHEN 1 THEN 'Online' 
        WHEN 2 THEN 'Ingame' 
        ELSE 'Offline' 
       END AS OnlineStatus
FROM dbo.WebUsers W
WHERE W.[Status]=1
GROUP BY OnlineStatus

Answer 1

使用子查询做得最好：

SELECT OnlineStatus, count(*)
FROM (
    SELECT  CASE dbo.fnGetWebUserOnlineStatus(W.Id) 
        WHEN 1 THEN 'Online' 
        WHEN 2 THEN 'Ingame' 
        ELSE 'Offline' 
         END AS OnlineStatus
    FROM dbo.WebUsers W
    WHERE W.[Status]=1
) sub
GROUP BY OnlineStatus

Answer 2

如果使用内部选择，它应该有效：

SELECT OnlineStatus, COUNT(*)
FROM (
    SELECT  CASE dbo.fnGetWebUserOnlineStatus(W.Id) 
                WHEN 1 THEN 'Online' 
               WHEN 2 THEN 'Ingame' 
               ELSE 'Offline' 
           END AS OnlineStatus
           FROM dbo.WebUsers W
           WHERE W.[Status]=1
) AS T1
GROUP BY OnlineStatus

Answer 3

您也可以将CASE WHEN移至COUNT

伪代码：

SELECT 
    COUNT(CASE dbo.fnGetWebUserOnlineStatus(W.Id) WHEN 1 THEN 1 ELSE NULL END) as OnlineCount,
    COUNT(CASE dbo.fnGetWebUserOnlineStatus(W.Id) WHEN 2 THEN 1 ELSE NULL END) as IngameCount ...
FROM dbo.WebUsers W 
WHERE W.[Status]=1

Microsoft SQL Count问题

3 个答案: