Question

我有一张表格，其中包含动物和数字这样的字段：

    Horse   1
    Mouse   2
    Cat     2
    Horse   4
    Cat     2
    Mouse   1
    Horse   1
    Horse   3
    Mouse   2
    Cat     1

现在，我想为每种动物获得最常见的价值。所以我期望这个结果：

Horse   1
Mouse   2
Cat     2

是否可以通过一个mySQL查询执行此操作？我不知道该怎么办。

Answer 1

对于8.0之前的版本：

select distinct a.animal, (
  select b.number
  from animals b
  where b.animal = a.animal
  group by b.animal, b.number
  order by count(*) desc
  limit 1
) as number
from animals a;

Demo

对于MySQL 8.0（或MariaDB 10.2）：

with count_all as (
  select animal, number, count(*) as cnt
  from animals
  group by animal, number
), count_max as (
  select animal, max(cnt) as cnt
  from count_all
  group by animal
)
select animal, number
from count_all
natural join count_max

Demo

注意：如果有关系-每个动物的第一个查询将仅返回一行。第二个将全部返回（并列）。您没有指定在这种情况下该怎么做。

如Juan Carlos Oropeza所指出的那样-在MySQL 8中，您还可以使用窗口函数ROW_NUMBER()或RANK()

with count_all as (
  select animal, number, count(*) as cnt
  from animals
  group by animal, number
), count_max as (
  select animal, number,
    row_number() over (partition by animal order by cnt desc) as rn
  from count_all
)
select animal, number
from count_max
where rn = 1

这不会恢复联系。如果您想束缚行，只需将row_number()替换为rank()。

Answer 2

您可以使用子查询来获取该信息：

SELECT c.animal,MAX(c.cnt)
FROM (
  SELECT t.animal, t.number, count(*) AS cnt
  FROM your_table t
  GROUP BY t.animal, t.number) c
GROUP BY c.animal

获取mysql中最常见的值

2 个答案: