sql - 如何重构此SQL查询？

我有一个名为users的表，其中有一个名为activated_at的列，我想通过检查该列是否为空来计算有多少用户被激活。然后像这样并排显示：

+----------+-----------+---------------+-------+
| Malaysia | Activated | Not Activated | Total |
+----------+-----------+---------------+-------+
| Malaysia |      5487 |           303 |  5790 |
+----------+-----------+---------------+-------+

这是我的SQL：

select "Malaysia",
    (select count(*) from users where activated_at is not null and locale='en' and  date_format(created_at,'%m')=date_format(now(),'%m')) as "Activated",
    (select count(*) from users where activated_at is null and locale='en' and  date_format(created_at,'%m')=date_format(now(),'%m')) as "Not Activated",
    count(*) as "Total"
    from users
    where locale="en"
    and  date_format(created_at,'%m')=date_format(now(),'%m');

在我的代码中，我必须三次指定所有where语句，这显然是多余的。我如何重构它？
当做，
马克。

最佳答案

不确定MySql是否支持CASE构造，但我通常通过以下方式处理此类问题：，

select "Malaysia",
    SUM(CASE WHEN activated_at is not null THEN 1 ELSE 0 END) as "Activated",
    SUM(CASE WHEN activated_at is null THEN 1 ELSE 0 END as "Not Activated",
    count(*) as "Total"
from users
where locale="en" and  date_format(created_at,'%m')=date_format(now(),'%m');