[Leetcode] [Database] Consecutive Numbers

题目如下:

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.

题目意思: 选出连续至少出现三次的数字

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解题思路: 三个表自连接，选出第一个，第二个，第三个来对比，如果相同则筛选出来

select distinct l1.Num     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;

题目意思理解了，这题目就觉得简单了.