Question

我有两个表registered和attended，每个表都有两列：AttendentId和SessionId。我想从这两个表中分别查询特定会话ID的AttendantId计数。

示例：

注册

AttendantId      SessionId    
ID1              SN1    
ID2              SN2
ID3              SN1
ID4              SN3

出席

AttendantId       SessionId    
ID1               SN1   
ID4               SN3

我想获得以下输出：

Count(Registered)   Count(Attended)  Session ID    
2                   1                SN1    
1                   0                SN2 
1                   1                SN3

Answer 1

您可以使用FULL OUTER JOIN：

select 
  coalesce(a.sessionid, r.sessionid) sessionid,
  count(r.AttendantId) countRegistered,
  count(a.AttendantId) countAttended
from registered r
full outer join attended a
  on r.sessionid = a.sessionid
  and r.AttendantId = a.AttendantId
group by coalesce(a.sessionid, r.sessionid);

请参阅SQL Fiddle with Demo

Answer 2

SELECT
    ISNULL(ACount, 0),
    ISNULL(RCount, 0),
    X.SessionId
FROM
    (
    SELECT SessionId FROM Registered
    UNION -- implies DISTINCT
    SELECT SessionId FROM Attended
    ) X
    LEFT JOIN
    (SELECT COUNT(*) AS RCount, SessionId
     FROM Registered
     GROUP BY SessionId) R ON X.SessionId = R.SessionId
    LEFT JOIN
    (SELECT COUNT(*) AS ACount, SessionId
     FROM Attended 
     GROUP BY SessionId) A ON X.SessionId = A.SessionId

SQLFiddle

Answer 3

尝试：

select count(distinct registered), 
       count(distinct attended), 
       SessionId
from (select AttendantId registered, null attended, SessionId
      from registered
      union all
      select null registered, AttendantId attended, SessionId
      from Attended) sq
group by SessionId

Answer 4

尝试此查询

select 
   a.sessionId, 
   case when aCnt is null then 0 else acnt end, 
   case when bCnt is null then 0 else bcnt end
from
   (select 
       sessionId, 
       count(*) aCNt 
   from 
       tbl1 
   group by 
       sessionid) a
full join
   (select 
       sessionId, 
       count(*) bCnt 
   from 
       tbl2 
   group by 
       sessionid) b
on 
   a.sessionId = b.sessionid

的 SQL FIDDLE ：

| SESSIONID | COLUMN_1 | COLUMN_2 | ----------------------------------- | SN1 | 2 | 1 | | SN2 | 1 | 0 | | SN3 | 1 | 1 |

希望这会有所帮助......

Answer 5

假设所有会话ID都存在于已注册的表中

SELECT Sum(CASE 
             WHEN a.attendentid IS NOT NULL THEN 1 
             ELSE 0 
           end) AS Count(registered), 
       Sum(CASE 
             WHEN b.attendentid IS NOT NULL THEN 1 
             ELSE 0 
           end) AS Count(attended), 
       a.sessionid 
FROM   registered a 
       INNER JOIN attended b 
               ON a.sessionid = b.sessionid 
GROUP  BY a.sessionid

将SQL连接与count结合使用

注册

出席

5 个答案:

的 SQL FIDDLE ：