MySQL - 為具有不同條件的組中的每一行獲取count（）

Question

我有一個高分表scores: (id int, deviceid int, value int, board int) 。 我想為特定玩家展示一個位置。 目前我正在這樣做（在PHP中）：

我選擇所有玩家都有得分和得分的棋盤：

select board, min(value) as value
from scores
where deviceid = 1234
group by board

然后對於每一行（$ board，$ value）我選擇：

select count(id) from scores
where board = $board and value < $value

通過選擇得分低於指定值的特定棋盤的行數，我得到玩家的位置（第一個玩家獲得位置0，所以當顯示時它將增加1）

我知道這是非常低效的，所以我正在尋找一種更快的方法 。 它可以在帶有光標的存儲過程中完成，但對於100個板，我需要做最多1 + 100次選擇。

簡而言之，我想在偽sql中做這樣的事情：

select board, min(value) as val,
       count(id) from _this_group_ where value < val
from scores
where deviceid = 1234
group by board

Answer 1

SELECT scores.board, count(1) AS position
FROM scores
JOIN
  (SELECT board, MIN(value) AS value
   FROM scores
   WHERE deviceid = 1234
   GROUP BY board
  ) player_scores
ON scores.board = player_scores.board
WHERE scores.value < player_scores.value
GROUP BY scores.board

Answer 2

您可以嘗試以下方式：

SELECT a.board, b.val COUNT(1) AS cnt
FROM scores a
    INNER JOIN(
        SELECT board, MIN(value) as val
        FROM scores
        WHERE deviceid = 1234
        GROUP BY board
    ) b
     ON a.board = b.board
    AND a.value < b.val
WHERE a.deviceid = 1234
GROUP BY a.board;

要么

SELECT a.board, MIN(a.value) as val,
       (SELECT COUNT(1)
        FROM scores b
        WHERE b.board = a.board AND
        b.value < MIN(a.value)) AS cnt
FROM scores a
WHERE a.deviceid = 1234;