Question

我确定了我的疑问：

SELECT * 
FROM  `participation` 
LEFT JOIN parties ON parties.id = participation.party_id
WHERE  `riding_id` = 10001
AND  `election_id` = 41
ORDER BY num_votes DESC 
LIMIT 1

这准确地产生了我想要的结果。

结果是投票最多的一方。

现在我想在TABLE ridings 的每一行上执行相同的查询其中包含所有riding_id行。遇到麻烦了。

我不想加入另一个表 - 但是要遍历每一行并执行与上面相同的计算 - 每行。

类似的东西：

SELECT * 
    FROM  `participation` 
    LEFT JOIN parties ON parties.id = participation.party_id
    WHERE  `riding_id` = "LOOP ALL riding_id IN ridings TABLE"
    AND  `election_id` = 41
    ORDER BY num_votes DESC 
    LIMIT 1

任何帮助都将不胜感激。

Answer 1

使用子查询很有吸引力：

SELECT * 
FROM  participation LEFT JOIN
      parties
      ON parties.id = participation.party_id
WHERE  riding_id IN (SELECT riding_id FROM ridings) AND
       election_id = 41
ORDER BY num_votes DESC

但是，你不再获得最高票数。你得到了一切。

以下是使用变量获取每个riding_id的最高投票数的方法：

SELECT *
FROM (SELECT *,
             (@rn := if(@r = riding_id, @rn + 1,
                        if(@rn := riding_id, 1, 1)
                       )
             ) as seqnum
      FROM  participation LEFT JOIN
            parties
            ON parties.id = participation.party_id CROSS JOIN
            (SELECT @rn := 0, @r := -1) params
      WHERE  riding_id IN (SELECT riding_id FROM ridings) AND
             election_id = 41
      ORDER BY riding_id, num_votes DESC 
     ) pp
WHERE seqnum = 1;

mysql对另一个表上的所有行执行相同的计算

1 个答案: