Question

我有两列日期t_date和s_date。我正在计算s_date与t_date的日期相同或在t_date发生后的n天窗口内发生的记录数。

这是查询。它返回多行。

select count(id)
from customers
where s_date >= t_date
and s_date <= t_date + 1
group by t_date;

有没有办法设计一个包含多个sub queries的查询，每个查询返回多行？这样我可以增加时间窗口？类似的东西：

select (
    select count(id)
    from customers
    where s_date >= t_date
    and s_date <= t_date + 1
    group by t_date
    ) as c1,
    (
    select count(id)
    from customers
    where s_date >= t_date
    and s_date <= t_date + 2
    group by t_date
    ) as c2;

但是，此查询会返回“Sub query returns more than 1 row”错误。

Answer 1

您可以使用CASE表达式：

SELECT
  SUM(CASE WHEN s_date >= t_date AND s_date <= t_date + 1 THEN 1 ELSE 0 END) AS c1, 
  SUM(CASE WHEN s_date >= t_date AND s_date <= t_date + 2 THEN 1 ELSE 0 END) AS c2
  ...
FROM customers
GROUP BY t_date;

mysql查询，子查询返回多行

1 个答案: