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.

思路：

自己没看题解做出来的第一道middle难度的题目，这个题和Rasing Temprature很像，考察的都是一个表中不同元组之间的某些属性的比较

那个easy的题目只要比较连续的两行就好，而这个题目要比较三行

将easy题目的两种解法套用过来，其中一个会超时，及O（2n^2）时间复杂度的那个嵌套选择算法，我分析这种算法之所以超时是因为每一次子select都要遍历整张表来判断where a.Id = c.Id - 2和where a.Id = b.Id-1，而当表的数据非常大的时候，速度就会很慢

第二种AC了的算法，感觉是一种消耗空间节省时间的方法，我们建立了表格之后，只需要遍历一遍就可以得出最后的答案。

AC代码：
select distinct a.Num as consecutiveNums

from Logs as a,Logs as b,Logs as c

where a.Id = b.Id - 1 and a.Id = c.Id - 2 and a.Num = b.Num and a.Num = c.Num

TLE代码：

select distinct a.Num as ConsecutiveNums

from Logs as a

where a.Num = (

select b.Num

from Logs as b

where a.Id = b.Id -1

)

and

a.Num = (

select c.Num

from Logs as c

where a.Id = c.Id -2

)