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 |
+-----------------+
# Write your MySQL query statement below
SELECT DISTINCT
l1.Num AS ConsecutiveNums
FROM
Logs l1,
Logs l2,
Logs l3
WHERE
l1.Id = l2.Id - 1
AND l2.Id = l3.Id - 1
AND l1.Num = l2.Num
AND l2.Num = l3.Num
;
窗口函数：lead()
lead函数在Impala中可以配合over使用，lead函数有三个参数
lead(property,num,default)第一个参数「property」标识想查询的列，「num」标识相对于当前行的第num行，第三个参数是默认值。
举例：
执行
SELECT id,lead(id,1,999) over(order by id) as next_id观察结果
可见实现了我们获取当前 id 下一个id的需求
所以本题的窗口函数写法：
# Write your MySQL query statement below
select distinct num as ConsecutiveNums from
(
select num,lead(num,1)over()as num1,lead(num,2)over()as num2
from logs
) as c
where c.num = c.num1 and c.num1 = c.num2