数据库练习——leetcode（180）：连续出现的数字

连续出现的数字

题目

解析

首先一定要非常明确的是本题是要找连续出现的数字，连续！
如何判断连续，通过ID来判断，

步骤一：将表复制三份，分别命名为l1,l2,l3

select * from Logs as l1, Logs as l2, logs as l3

这个的效果为两个表相连接了，笛卡尔连接，一个ID对应另一个表的全部ID，效果如下：

步骤二：找到连续的学号：

select * from Logs as l1, Logs as l2, logs as l3
where l1.id = l2.id-1 and l2.id = l3,id-1

效果如下

步骤三：找到出现三以上相等的数字

select * from Logs as l1, Logs as l2, logs as l3
where l1.id = l2.id-1 and l2.id = l3.id-1
and l1.num = l2.num and l2.num =l3.num

步骤四：取出要找的结果

select distinct l1.Num as ConsecutiveNums from Logs as l1,Logs as l2,Logs as l3 where l1.id = l2.id-1 and l2.id = l3.id-1
and l1.Num = l2.Num and l2.Num = l3.Num

归纳：

select distinct l1.Num as ConsecutiveNums 
from Logs as l1,Logs as l2,Logs as l3 
where l1.id = l2.id-1 and l2.id = l3.id-1
and l1.Num = l2.Num and l2.Num = l3.Num