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

题意:求表中连续出现3次以上的数据.

因此，根据题意构造第一版本答案（使用连续的ID进行比较）:

# Write your MySQL query statement below
SELECT DISTINCT t1.Num AS ConsecutiveNums 
    FROM 
        Logs t1,
        Logs t2,
        Logs t3
    WHERE 
        t1.Id = t3.Id - 1
        AND t2.Id = t3.Id + 1
        AND t1.Num = t2.Num
        AND t2.Num = t3.Num;

当前版本答案通过了测试，但是运行效率太低了.
分析原因，可能与t1.Id = t3.Id - 1条件相关，当t3.Id为0时，-1不会寻找到相关数据，导致sql执行缓慢.
因此，修改为如下所示：

# Write your MySQL query statement below
# Write your MySQL query statement below
SELECT DISTINCT t1.Num AS ConsecutiveNums 
    FROM 
        Logs t1,
        Logs t2,
        Logs t3
    WHERE 
        t2.Id = t1.Id + 1
        AND t3.Id = t1.Id + 2
        AND t1.Num = t2.Num
        AND t2.Num = t3.Num;

此版本，效率得到了巨大的提高。