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               |
+-----------------+

本题也是对join使用的考察。与175. Combine Two Tables类似。join的用法在175. Combine Two Tables中有记录。

select 
distinct l1.num as ConsecutiveNums
from logs l1 
inner join logs l2 
on l1.ID+1 = l2.ID 
inner join logs l3 
on l2.ID+1 = l3.ID
where l1.num = l2.num and l1.num = l3.num