题目：
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 |
±----------------+
Create table If Not Exists Logs (Id int,Num int);
Truncate table Logs;
insert into Logs (Id, Num) values ('1','1');
insert into Logs (Id, Num) values ('2','1');
insert into Logs (Id, Num) values ('3', '1');
insert into Logs (Id, Num) values ('4','2');
insert into Logs (Id, Num) values ('5','1');
insert into Logs (Id, Num) values ('6','2');
insert into Logs (Id, Num) values ('7','2');
答案
select distinct l1.Num ConsecutiveNums from Logs l1
left join Logs l2 on l1.Id = l2.Id - 1
left join Logs l3 on l1.Id = l3.Id - 2
where l1.Num = l2.Num and l2.Num = l3.Num;
知识点1：表名 表别名
Logs l1
知识点2：列名 列别名
l1.Num ConsecutiveNums