如何獲得每組的最大行數？

Question

我有一個數據庫，其中人們在不同的地方提交投票。在特定的時間，我想知道誰在每個地方獲得了最多的選票。 （一個人可以在兩個不同的地方進行表決）

這是SQL我到目前爲止：

SELECT placeId, userVotedId, cnt 
FROM 
    (SELECT uvo.userVotedId, p.placeId, count(*) as cnt 
    FROM users as u, users_votes as uvo, places as p 
    WHERE u.userId = uvo.userVotedId 
     AND p.placeId = uvo.placeId 
    GROUP BY userVotedId, placeId) 
AS RESULT 

，給了我這樣的結果：

現在，這些都我真正想要的行：

我的查詢缺少什麼，所以我可以得到這個？

• 我想每個地方都有一個結果。所以我應該只看到不同的placeIds，用userVotedId獲得最多的選票。

• 在平局的情況下，隨機獲勝者將會這樣做！

Answer 1

好像你還需要一個集合體。使用您 cnt價值和 GROUP BY placeId, userVotedId的 MAX()合計：

SELECT placeId, userVotedId, max(cnt) 
FROM 
(
    SELECT uvo.userVotedId, p.placeId, count(*) as cnt 
    FROM users as u 
    INNER JOIN users_votes as uvo 
    ON u.userId = uvo.userVotedId 
    INNER JOIN places as p 
    ON p.placeId = uvo.placeId 
    GROUP BY userVotedId, placeId 
) AS RESULT 
GROUP BY placeId, userVotedId 

注：我改變了你的查詢中使用 JOIN語法，而不是表之間的逗號。

編輯，根據您的評論下面應該工作：

select total.uservotedid, 
    total.placeid, 
    total.cnt 
from 
(
    SELECT uvo.userVotedId, p.placeId, count(*) as cnt 
    FROM users as u 
    INNER JOIN users_votes as uvo 
    ON u.userId = uvo.userVotedId 
    INNER JOIN places as p 
    ON p.placeId = uvo.placeId 
    GROUP BY userVotedId, placeId 
) total 
inner join 
(
    select max(cnt) Mx, placeid 
    from 
    (
    SELECT uvo.userVotedId, p.placeId, count(*) as cnt 
    FROM users as u 
    INNER JOIN users_votes as uvo 
     ON u.userId = uvo.userVotedId 
    INNER JOIN places as p 
     ON p.placeId = uvo.placeId 
    GROUP BY userVotedId, placeId 
) mx 
    group by placeid 
) src 
    on total.placeid = src.placeid 
    and total.cnt = src.mx 

見SQL Fiddle with Demo

結果是：

| USERVOTEDID | PLACEID | CNT | 
------------------------------- 
|   65 |  11 | 1 | 
|   67 |  13 | 1 | 
|   67 |  25 | 1 | 
|   67 |  51 | 2 | 

編輯＃2，如果你想有一個隨機數如果有聯繫返回，那麼你可以使用用戶變量：

select uservotedid, 
    placeid, 
    cnt 
from 
(
    select total.uservotedid, 
    total.placeid, 
    total.cnt, 
    @rownum := case when @prev = total.placeid then @rownum+1 else 1 end rownum, 
    @prev := total.placeid pplaceid 
    from 
    (
    SELECT uvo.userVotedId, p.placeId, count(*) as cnt 
    FROM users as u 
    INNER JOIN users_votes as uvo 
     ON u.userId = uvo.userVotedId 
    INNER JOIN places as p 
     ON p.placeId = uvo.placeId 
    GROUP BY userVotedId, placeId 
) total 
    inner join 
    (
    select max(cnt) Mx, placeid 
    from 
    (
     SELECT uvo.userVotedId, p.placeId, count(*) as cnt 
     FROM users as u 
     INNER JOIN users_votes as uvo 
     ON u.userId = uvo.userVotedId 
     INNER JOIN places as p 
     ON p.placeId = uvo.placeId 
     GROUP BY userVotedId, placeId 
    ) mx 
    group by placeid 
) src 
    on total.placeid = src.placeid 
    and total.cnt = src.mx 
    order by total.placeid, total.uservotedid 
) src 
where rownum = 1 
order by placeid, uservotedid 

見SQL Fiddle with Demo

Answer 2

SELECT placeId, userVotedId, MAX(cnt) 
    FROM (SELECT uvo.userVotedId, p.placeId, count(*) AS cnt 
      FROM users as u, users_votes as uvo, places as p 
      WHERE u.userId = uvo.userVotedId AND p.placeId = uvo.placeId 
      GROUP BY userVotedId, placeId) AS RESULT 
    GROUP BY placeId 

• 類似的問題 - SQL query max(), count()

• Demo

Answer 3

爲簡單起見，我叫你的查詢測試：

SELECT * 
FROM Test T JOIN (
SELECT t.placeId, Max(t.cnt) maxcnt 
FROM Test t 
GROUP BY t.placeId) T2 ON T.placeId = T2.placeId and T.cnt = T2.maxcnt 

這裏是Fiddle。

BTW - 測試=：

SELECT uvo.userVotedId, p.placeId, count(*) as cnt 
    FROM users as u 
    INNER JOIN users_votes as uvo 
    ON u.userId = uvo.userVotedId 
    INNER JOIN places as p 
    ON p.placeId = uvo.placeId 
    GROUP BY userVotedId, placeId 

好運。

- 編輯 - 的要求，這裏是最後的代碼：你想要什麼，你得到什麼

SELECT * 
FROM (SELECT uvo.userVotedId, p.placeId, count(*) AS cnt 
      FROM users as u, users_votes as uvo, places as p 
      WHERE u.userId = uvo.userVotedId AND p.placeId = uvo.placeId 
      GROUP BY userVotedId, placeId) T JOIN (
SELECT t.placeId, Max(t.cnt) maxcnt 
FROM (SELECT uvo.userVotedId, p.placeId, count(*) AS cnt 
      FROM users as u, users_votes as uvo, places as p 
      WHERE u.userId = uvo.userVotedId AND p.placeId = uvo.placeId 
      GROUP BY userVotedId, placeId) t 
GROUP BY t.placeId) T2 ON T.placeId = T2.placeId and T.cnt = T2.maxcnt