如何使用postgresql中的不同WHERE语句按group by进行两次单独计数？

我有两个单独的问题，只是在“WHERE”语句中有所不同：

SELECT concat(extract(MONTH from created_at),'-', extract(year from created_at)) AS "Month", 
count(email) AS "Total AB Signups"
from users
where is_accountant='t'
group by 1,extract(month from created_at),extract(year from created_at)
order by extract(year from created_at),extract(month from created_at);

然后：

如何将其合并到一个如下所示的表中：

Month | Total AB Signups | Total SMB Signups
---------------------------------------------

---

您可以将

where

条件移动到count函数中的

case

表达式：

SELECT concat(extract(MONTH from created_at),'-', extract(year from created_at)) AS "Month", 
count(case when is_accountant='t' then email end) AS "Total AB Signups",
count(case when is_accountant='f' then email end) AS "Total SMB Signups"
from users
group by 1,extract(month from created_at),extract(year from created_at)
order by extract(year from created_at),extract(month from created_at);

或者，如果您使用的是Postgresql 9.4+，则可以使用新的

过滤器

语法：

SELECT concat(extract(MONTH from created_at),'-', extract(year from created_at)) AS "Month", 
count(email) FILTER (where is_accountant='t') AS "Total AB Signups",
count(email) FILTER (where is_accountant='f') AS "Total SMB Signups"
from users
group by 1,extract(month from created_at),extract(year from created_at)
order by extract(year from created_at),extract(month from created_at);

---

在第二次查询中，列名也是

Total AB Signups

，但在所需结果中是

Total SMB Signups

；我猜这是一个打字错误，不是故意的？非常感谢！这非常有帮助。顺便说一句，你介意看看我今天发布的其他问题吗？

SELECT concat(extract(MONTH from created_at),'-', extract(year from created_at)) AS "Month", 
count(email) FILTER (where is_accountant='t') AS "Total AB Signups",
count(email) FILTER (where is_accountant='f') AS "Total SMB Signups"
from users
group by 1,extract(month from created_at),extract(year from created_at)
order by extract(year from created_at),extract(month from created_at);