Consecutive Numbers

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-问题描述：

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.
题目要求查找到连续出现次数大于等于3次的记录，这里需要注意的是对原表不需要排序，并且因为有连续出现3次以上的场景存在，所以需要对输出的记录用distinct来剔除重复的记录
以下参考了leetcode上的讨论区的内容：
https://leetcode.com/discuss/21562/solution-with-user-defined-variables

select DISTINCT num FROM(select num,    case       when @record = num then @count:=@count+1       when @record <> @record:=num then @count:=1 end as n    from         Logs,(select @count:=0,@record:=(select num from Logs limit 0,1)) r) awhere a.n>=3

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