我需要选择相同order_ID的所有值，其中第一个日期和最后一个日期之间的差异等于或小于7，但我无法弄清楚我应该怎么做，可以任何一个人给我一些帮助我应该怎么做？
数据库布局：
+---------------+---------------------+
| order_ID | date |
+---------------+---------------------+
| 1 | 2012-01-21 09:15:00 |
| 1 | 2012-01-21 09:15:00 |
| 2 | 2012-01-21 14:15:00 |
| 3 | 2012-01-22 10:05:00 |
| 3 | 2012-01-22 10:05:00 |
| 4 | 2012-01-22 14:25:00 |
| 5 | 2012-01-25 11:05:00 |
| 6 | 2012-01-27 16:10:00 |
| 6 | 2012-01-27 16:10:00 |
| 7 | 2012-01-27 16:10:00 |
| 8 | 2012-01-28 15:55:00 |
| 9 | 2012-01-28 16:40:00 |
| 10 | 2012-01-28 17:35:00 |
| 10 | 2012-01-28 17:35:00 |
| 10 | 2012-02-03 09:35:00 |
| 12 | 2012-02-03 10:15:00 |
| 13 | 2012-02-05 13:25:00 |
| 14 | 2012-02-05 13:45:00 |
| 15 | 2012-02-05 14:10:00 |
| 15 | 2012-02-05 14:10:00 |
| 16 | 2012-02-07 15:45:00 |
| 17 | 2012-02-11 11:50:00 |
| 18 | 2012-02-11 12:45:00 |
| 19 | 2012-02-14 09:10:00 |
| 19 | 2012-02-16 13:05:00 |
| 19 | 2012-02-16 13:05:00 |
| 20 | 2012-02-17 09:40:00 |
| 21 | 2012-02-19 14:10:00 |
| 21 | NULL |
| 22 | 2012-02-25 10:20:00 |
| 23 | 2012-02-25 11:05:00 |
| 24 | 2012-02-25 13:35:00 |
| 25 | 2012-02-27 17:10:00 |
| 26 | 2012-03-03 09:40:00 |
| 27 | 2012-03-05 10:45:00 |
| 28 | NULL |
| 29 | NULL |
| 29 | NULL |
| 29 | NULL |
| 30 | NULL |
| 30 | NULL |
+---------------+---------------------+
答案 0 :(得分：4)
您需要决定如何处理空值（合并到最大或最小日期值？），但这应该为您提供查询的基本结构。
select order_id
from (
select order_id, min(date) as mindate, max(date) as maxdate
from tbl
group by order_id) t
where datediff(maxdate,mindate) <= 7