LeetCode——Consecutive Numbers

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

题意:求表中连续出现3次以上的数据.

因此，根据题意构造第一版本答案（使用连续的ID进行比较）:

# Write your MySQL query statement belowSELECT DISTINCT t1.Num AS ConsecutiveNums     FROM         Logs t1,        Logs t2,        Logs t3    WHERE         t1.Id = t3.Id - 1        AND t2.Id = t3.Id + 1        AND t1.Num = t2.Num        AND t2.Num = t3.Num;

当前版本答案通过了测试，但是运行效率太低了.
分析原因，可能与t1.Id = t3.Id - 1条件相关，当t3.Id为0时，-1不会寻找到相关数据，导致sql执行缓慢.
因此，修改为如下所示：

# Write your MySQL query statement below# Write your MySQL query statement belowSELECT DISTINCT t1.Num AS ConsecutiveNums     FROM         Logs t1,        Logs t2,        Logs t3    WHERE         t2.Id = t1.Id + 1        AND t3.Id = t1.Id + 2        AND t1.Num = t2.Num        AND t2.Num = t3.Num;

此版本，效率得到了巨大的提高。

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