Question

我在PostgreSQL中有以下架构的表：

Category    |   Type 
------------+---------
A           |   0 
C           |   11 
B           |   5 
D           |   1 
D           |   0 
F           |   2   
E           |   11 
E           |   9 
.           |   . 
.           |   .

如何选择类别最大类型？以下是我的全部内容：

SELECT 
    category, 
    type, 
    COUNT(*)
FROM 
    table
GROUP BY 
    category, 
    type
ORDER BY 
    category, 
    count 
    DESC

我的预期结果是这样的：

Cat | Type | Count
  -------- + ------- + ------

A | 0 | 5

B | 5 | 30

C | 2 | 20

D | 3 | 10

这是每个类别中出现最大值的类型，包含该类型的计数。

Answer 1

您可以使用以下查询：

SELECT category, type, cnt
FROM (
   SELECT category, type, cnt,
          RANK() OVER (PARTITION BY category 
                       ORDER BY cnt DESC) AS rn
   FROM (
      SELECT category, type, COUNT(type) AS cnt
      FROM mytable
      GROUP BY category, type ) t
) s
WHERE s.rn = 1

以上查询使用您在OP中发布的自己的查询，并对其应用RANK()窗口函数。使用RANK()，我们可以指定来自初始查询的具有最大COUNT(type)值的所有记录。

注意：如果有多个类型具有特定类别的最大出现次数，则上述查询将返回所有的类型，如使用RANK的结果。

Demo here

Answer 2

如果我理解正确，你可以使用窗口功能：

SELECT category, type, cnt
FROM (SELECT category, type, COUNT(*) as cnt,
             ROW_NUMBER() OVER (PARTITION BY type ORDER BY COUNT(*) DESC) as seqnum
      FROM table
      GROUP BY category, type
     ) ct
WHERE seqnum = 1;

Answer 3

SELECT 
    category, 
    type, 
    COUNT(*)
FROM 
    table
GROUP BY 
    category, 
    type
HAVING 
    COUNT(*) = (SELECT MAX(C) FROM (SELECT COUNT(*) AS C FROM A GROUP BY A) AS Q)

EDITED：我向读者道歉，

COUNT(*) = (SELECT MAX(COUNT(*)) FROM table GROUP BY category,type)

是ORACLE版本，postgresql版本是：

COUNT(*) = (SELECT MAX(C) FROM (SELECT COUNT(*) AS C FROM A GROUP BY A) AS Q)

Answer 4

SELECT类别，MAX（Occurence） FROM（SELECT t.category as category，Count（*）AS Occurence FROM table t）;

Answer 5

SELECT 
    category, 
    type, 
    COUNT(*) AS count
FROM 
    table
GROUP BY 
    category, 
    type
ORDER BY 
    category ASC

如何在PostgreSQL中选择最大计数

5 个答案: