mysql – 在sql中组合多个计数查询

我有一个用户的表,其中有3列,我正在尝试计数,然后按created_at日期分组.

列：’created_at’,’answers_count’,’questions_count’

如何将这3个查询合并为一个,并将所有计数按相同的created_at日期分组？

这是3个单独的查询：

-- daily new signups
SELECT date_trunc('day', users.created_at) AS signup_date, count(*) AS new_users
FROM users
GROUP BY signup_date
ORDER BY signup_date DESC;

-- new user answers_count by signup date
SELECT date_trunc('day', users.created_at) AS signup_date, count(*) AS answers_count
FROM users
WHERE users.answers_count > 0
GROUP BY signup_date
ORDER BY signup_date DESC;

-- new user questions_count by signup date 
SELECT date_trunc('day', users.created_at) AS signup_date, count(*) AS qs_received
FROM users
WHERE users.questions_count > 0
GROUP BY signup_date
ORDER BY signup_date DESC;

解决方法:

您应该尝试使用带有CASE的SUM()来完成此任务.

尝试这样的事情：

SELECT date_trunc('day', users.created_at) AS signup_date, 
  count(*) AS new_users,
  sum(case when answers_count > 0 then 1 else 0 end) as answers_count,
  sum(case when questions_count > 0 then 1 else 0 end) as qs_received,
FROM users
GROUP BY signup_date
ORDER BY signup_date DESC;