180. 连续出现的数字

题目描述

编写一个 SQL 查询，查找所有至少连续出现三次的数字。

+----+-----+
| Id | Num |
+----+-----+
| 1  |  1  |
| 2  |  1  |
| 3  |  1  |
| 4  |  2  |
| 5  |  1  |
| 6  |  2  |
| 7  |  2  |
+----+-----+
例如，给定上面的 Logs 表， 1 是唯一连续出现至少三次的数字。

+-----------------+
| ConsecutiveNums |
+-----------------+
| 1               |
+-----------------+

分析

通过子查询来实现。
子查询通过变量构造。
子查询的构造：遍历，Num相等的计数器加一。

代码

select distinct Num as ConsecutiveNums 
    from ( 
        select @count := if(@prev = Num, @count + 1, 1) as c, Num, @prev := Num 
            from Logs , (select @count := 0, @prev :=1) init 
    ) t where t.c >= 3;
    

题目链接

https://leetcode-cn.com/problems/consecutive-numbers/description/