Question

我有两个单独的查询，只在“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：

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='f'
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);

我如何将其合并到一个看起来像这样的表中：

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

Answer 1

您可以将where条件移动到count函数内的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filter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);

如何在postgresql中使用不同的WHERE语句按组进行两个单独的计数？

1 个答案: