如何在SQL中使用多个COUNT

Question

在我的餐桌上task,每个人task都有state.

1 - planned
2 - executing
3 - finished

我想要计算所有计划,执行和完成task.

我可以写三个这样的查询:

SELECT COUNT(*) FROM `task` WHERE state = 1
SELECT COUNT(*) FROM `task` WHERE state = 2
SELECT COUNT(*) FROM `task` WHERE state = 3

所以,我的问题是:有可能(以及如何？)在一个查询中获取此数据？

感谢您的任何帮助.

Answer 1

另一种方法是使用group by,如下所示:

select state, count(*)
from task
group by state

Answer 2

你使用SUM

select state,
sum(case when state = 1 then 1 else 0 end) state1count,
sum(case when state = 2 then 1 else 0 end) state2count,
sum(case when state = 3 then 1 else 0 end) state3count
from task