Question

我有如下表格：

Car(id, make, ....)
Deal(id,datetime,car_id,....)

我想写一个会返回一年的查询，以及一辆汽车可以获得交易最多的汽车（即最多的交易ID）以及该汽车的交易数量。

我开始了，

SELECT YEAR(D.datetime) AS the_year, C.make, COUNT(D.id) AS num
FROM Deal D, Car C
WHERE D.car_id=C.id
GROUP BY the_year

不幸的是，这已经回归了当年和交易总数。所以我想在另一个表中创建它，然后调用MAX(tbl.num)，但我对语法感到困惑有人可以帮帮我吗？

Answer 1

这是一个有趣的问题。您正在寻找的是特别称为＆＃34;模式＆＃34;在统计中。在MySQL中，你可以通过使用变量或group_conat() / substring_index（）`技巧来实现这一点。我将展示后者：

SELECT the_year,
       substring_index(group_concat(cd.make order by num desc), ',', 1) as the_mark
FROM (SELECT YEAR(D.datetime) AS the_year, C.make, COUNT(D.id) AS num
      FROM Deal D JOIN
           Car C
           ON D.car_id = C.id
      GROUP BY the_year, c.make
     ) cd
GROUP BY the_year;

编辑：

使用变量的版本：

SELECT the_year,
       substring_index(group_concat(cd.make order by num desc), ',', 1) as the_mark
FROM (SELECT YEAR(D.datetime) AS the_year, C.make, COUNT(D.id) AS num,
             @rn := if(@year = YEAR(D.datetime), @rn + 1, 1) as rn,
             @year := YEAR(D.datetime)
      FROM Deal D JOIN
           Car C
           ON D.car_id = C.id CROSS JOIN
           (SELECT @year := 0, @rn := 0) vars
      GROUP BY the_year, c.make
      ORDER BY the_year, num DESC
     ) cd
WHERE rn = 1;

在SQL中找到每年租得最多的汽车

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