Mysql通过分组计算不同的列

Question

我有一个表格，其中每一行代表一个带有 id、日期和原因的更正

id | date                | causes
___________________________________

1  | 2018-01-29 08:49:19 | crash
2  | 2018-08-08 10:03:37 | timeout
3  | 2018-06-26 07:48:12 | other

我使用这个sql请求来获取每月修正的次数

SELECT YEAR(date) Year, MONTH(date) Month, count(*) Total FROM correction group by YEAR(date), MONTH(date)

它给了我这样的结果

Year | Month | Total
____________________

2018 |   1   | 42
2018 |   2   | 69
2018 |   3   | 50

是否可以修改请求以获取每个原因的结果数量并获得如下结果：

 Year | Month | Total | crash | timeout | other
 ____________________________________________

 2018 |   1   | 42   | 10     | 12      | 20
 2018 |   2   | 69   | 9      | 50      | 10
 2018 |   3   | 50   | 10     | 20      | 20

Answer 1

你需要条件聚合：

SELECT YEAR(date) Year, MONTH(date) Month, COUNT(*) Total,
       SUM(causes = 'crash') crash,
       SUM(causes = 'timeout') timeout,
       SUM(causes = 'other') other
FROM correction c 
GROUP BY YEAR(date), MONTH(date);