Question

我有一个MySQL表'tbl_words'，如下所示：

+----+-------+---------+
| id | name  | word    |
+----+-------+---------+
|  1 | Bob   | rabbit  |
|  2 | Bob   | hare    |
|  3 | Bob   | hare    |
|  4 | Bob   | chicken |
|  5 | Paul  | goose   |
|  6 | Paul  | chicken |
|  7 | Paul  | rabbit  |
|  8 | Paul  | hare    |
|  9 | Paul  | hare    |
| 10 | Paul  | chicken |
| 11 | Paul  | goose   |
| 12 | Laura | goose   |
| 13 | Laura | rabbit  |
| 14 | Laura | rabbit  |
| 15 | Laura | goose   |
| 16 | Laura | fox     |
+----+-------+---------+

我想为每个列'name'获得两个最常见的列'word'。我可以通过查询获得的最接近的是：

SELECT name, word, COUNT(*) AS magnitude 
FROM tbl_words 
GROUP BY name, word 
ORDER BY magnitude DESC
LIMIT 2

返回：

+-------+---------+-----------+
| name  | word    | magnitude |
+-------+---------+-----------+
| Paul  | chicken |         2 |
| Laura | rabbit  |         2 |
+-------+---------+-----------+

但是我正在寻找这个：

+-------+---------+-----------+
| name  | word    | magnitude |
+-------+---------+-----------+
| Bob   | hare    |         2 |
| Bob   | chicken |         1 |
| Paul  | chicken |         2 |
| Paul  | goose   |         2 |
| Laura | rabbit  |         2 |
| Laura | goose   |         2 |
+-------+---------+-----------+

我如何实现这一目标，即获得每个名字最常用的两个单词？

Answer 1

我还没有通过测试，但您的查询应该如下：

    SELECT name, word, COUNT(*) AS magnitude 
    FROM tbl_words where name in 
(select name from   tbl_words ORDER BY magnitude DESC LIMIT 2)
    GROUP BY name, word

Answer 2

你想要每组最大的n，所以只需要计算它并按照这样的方式进行过滤

SELECT name, word, magnitude 
FROM(
    SELECT name, word, magnitude, IF(@a = name, @b := @b + 1, @b := 1) counting, @a := name
    FROM(
        SELECT name, word, COUNT(*) AS magnitude 
        FROM tbl_words 
        GROUP BY name, word
        ORDER BY name, magnitude DESC
    ) t
    CROSS JOIN(select @a := '', @b := 0)temp
)t1
WHERE counting <=3

DEMO

Answer 3

此查询将返回每个用户每个单词的出现次数：

SELECT name, word, COUNT(*) as cnt
FROM tbl_words
GROUP BY name, word

然后我们可以在这个子查询上使用GROUP_CONCAT，由cnt desc命令：

SELECT name, GROUP_CONCAT(word ORDER BY cnt DESC)
FROM (
  SELECT name, word, COUNT(*) as cnt
  FROM tbl_words
  GROUP BY name, word
) s
GROUP BY name

将返回以逗号分隔的所有单词列表，按cnt降序排列。

然后您可以使用SUBSTRING_INDEX获取前两个单词：

SELECT name, SUBSTRING_INDEX(GROUP_CONCAT(word ORDER BY cnt DESC), ',', 2) most_frequent
FROM (
  SELECT name, word, COUNT(*) as cnt
  FROM tbl_words
  GROUP BY name, word
) s
GROUP BY name

请记住，如果两个以上的单词具有相同的频率，则会选择两个随机单词。

在MySQL查询中返回分组的组

3 个答案: