180. Consecutive Numbers
Write a SQL query to find all numbers that appear at least three times consecutively.
+—-+—–+
| Id | Num |
+—-+—–+
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 2 |
| 5 | 1 |
| 6 | 2 |
| 7 | 2 |
+—-+—–+
+—-+——-+
For example, given the above Logs table, 1 is the only number that appears consecutively for at least three times.
+—————–+
| ConsecutiveNums |
+—————–+
| 1 |
+—————–+
解答：这道题有点点坑，因为没有说明Id是否连续，虽然题目默认是连续的。
一开始没有申请题，认为只是提取数量超过3个的，用了下面这个查询语句：
SELECT Num AS ConsecutiveNums from Logs GROUP BY Num HAVING COUNT(Num) >3题目的关键在于连续取三行数据，且要保证数目相等，ID默认连续，语句如下：
SELECT l1.Num AS ConsecutiveNums from Logs l1,Logs l2,Logs l3
WHERE l1.num =l2.num AND l2.num=l3.num AND l1.Id = l2.Id+1 AND l2.Id = l3.Id+1等于数据表自身内连接了两次，取数字相同且ID连续3个的记录。