单个查询中的不同计数

Question

我有一张这样的桌子：

---------------------- |姓名 |日期 | ---------------------- |约翰 |七月 | |卡尔 |八月 | |约翰 |七月 | |罗伯特 |八月 | |卡尔 |九月 | |约翰 |八月 | |卡尔 |八月 | |约翰 |七月 | |罗伯特 |九月 | |卡尔 |八月 | ----------------------

我想按月份计算姓名。

选择名称， COUNT(IF(`Date` = 'July',1,0)) AS 七月， COUNT(IF(`Date` = 'August',1,0)) AS 八月， COUNT(IF(`Date` = 'September',1,0)) AS 9 月， COUNT(*) AS All FROM 表 按名称分组

我试过这个查询，但是计数值都一样

Answer 1

发生这种情况的原因很简单：COUNT() 只计算值的出现次数。 （= 数据集中有多少个值？）

这样看，0 只是另一个值，就像 1 一样。

你可以这样做：

SELECT Name, 
COUNT(IF(`Date` = 'July', 1, NULL)) AS July,
COUNT(IF(`Date` = 'August', 1, NULL)) AS August,
COUNT(IF(`Date` = 'September', 1, NULL)) AS September,
COUNT(*) AS All FROM table
GROUP BY Name

这是可行的，因为像 COUNT() 这样的聚合函数会忽略 NULL 值。

或者，正如其他人回答的那样，您可能只是 SUM() 所有 1 值：

SELECT Name, 
SUM(`Date` = 'July') AS July,
SUM(`Date` = 'August') AS August,
SUM(`Date` = 'September') AS September,
COUNT(*) AS All FROM table
GROUP BY Name

这写得更短了，因为评估 field = value 已经返回 1 如果它匹配或 0 否则。无需包装 IF() 即可完成相同的操作。

Answer 2

SELECT name,
  SUM(IF(`month` = 'July',1,0)) AS July,
  SUM(IF(`month` = 'August',1,0)) AS August,
  SUM(IF(`month` = 'September',1,0)) AS September,
  COUNT(*)  FROM test
GROUP BY name;

参考：https://stackoverflow.com/a/13075582/1688441

Answer 3

你可以试试这个最简单的方法。 条件聚合函数与布尔（0或1）

SELECT Name, 
    SUM(`Date` = 'July') AS July,
    SUM(`Date` = 'August') AS August,
    SUM(`Date` = 'September') AS September,
    COUNT(*) AS All 
FROM table
GROUP BY Name

Answer 4

COUNT 计算非空值，试试SUM

SELECT Name, 
SUM(IF(`Date` = 'July',1,0)) AS July,
SUM(IF(`Date` = 'August',1,0)) AS August,
SUM(IF(`Date` = 'September',1,0)) AS September,
COUNT(*) AS All FROM table
GROUP BY Name

Answer 5

count 计算不是null 的值 - 包括零。使用ifs，您可以使用sum 来模拟count - 您将有效地计算1s 的值：

SELECT Name, 
SUM(IF(`Date` = 'July',1,0)) AS July,
SUM(IF(`Date` = 'August',1,0)) AS August,
SUM(IF(`Date` = 'September',1,0)) AS September,
SUM(*) AS All FROM table
GROUP BY Name

Answer 6

select date, count(*) 
from table1
group by date

应该给你类似的东西

|DATE       |Count(*)|
----------------------
|August     |    5   |
|July       |    3   |
|September  |    2   |

http://sqlfiddle.com/#!9/c0a483/2

Answer 7

试试SELECT Name, Date, Count(*) as Count FROM table GROUP BY Name,Date

它应该返回如下内容：

| Name  | Date      | Count |
-----------------------------
| Carl  | August    |   3   |
| Carl  | September |   1   |
| John  | July      |   3   |
| John  | August    |   1   |
| Robert| September |   1   |
| Rober | August    |   1   |

看到这个SQL Fiddle。