[LeetCode#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               |
+-----------------+

　　其实这道题的解法与我在这篇文章中有异曲同工之处：https://www.cnblogs.com/lsyb-python/p/11083828.html，这道题让我们找Num列中连续出现相同数字三次的数字，那么由于需要找三次相同数字，所以我们需要建立三个表的实例，我们可以有a、b和c内交，a和b的id下一个位置比，a和c的下两个位置比，然后将num都相同的数字返回即可：

SELECT a.Num FROM logs as a
JOIN logs as b ON a.Id = b.Id -1
JOIN logs as c on a.Id = c.Id -2
WHERE a.Num = b.Num AND b.Num = c.Num;