mysql - 如何计算相同事​​件的日差

Question

我的目标是GROUP (eid) SORT BY dayatime()，选择每组中的前2次，计算日差。

我知道这个想法，但是我怎样才能将它转化为真正的 MySQL 查询语法？

mysql> select * from events;
+------+------------+
| eid  | dt         |
+------+------------+
|    1 | 2013-01-01 | -> 3
|    1 | 2013-01-04 | -> 1
|    1 | 2013-01-05 |
|    2 | 2013-04-01 | -> 7
|    2 | 2013-04-08 |
+------+------------+
5 rows in set (0.00 sec)


GOAL: query that gives this result: 
+------+------------+-----------------+
| eid  | dt         | days_until_next |
+------+------------+-----------------+
|    1 | 2013-01-01 |               3 |
|    1 | 2013-01-04 |               1 |
|    2 | 2013-04-01 |               7 |

Answer 1

本质上，您需要lead()功能，但MySQL不支持此功能。相反，您可以使用相关子查询:

select e.eid, e.dt, datediff(next_dt, dt) as days_until_next
from (select e.*,
             (select dt
              from events e2
              where e2.eid = e.eid and e2.dt > e.dt
             ) as next_dt
      from events e
     ) e
where next_dt is not null;