[MySQL][LeetCode][Medium] 180. Consecutive Numbers

心得

這題要找出連續三次重複出現的數字，我原本一直在想如果中間有斷層(中間有資料被刪除)的話是否要先自己排序一次，結果看了一下Top Solutions才發現根本不用考慮這個問題，直接ID+1尋找下筆資料即可，既然這麼單純的話也沒什麼問題了。

問題

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.

答案

1. 方法對，但會TimeOut

   # Write your MySQL query statement below
   SELECT DISTINCT(a.Num) AS ConsecutiveNums
   FROM Logs AS a
   WHERE ( SELECT z.Num
           FROM Logs AS z
           WHERE z.Id = a.Id + 1) = a.Num
   AND (   SELECT z.Num
           FROM Logs AS z
           WHERE z.Id = a.Id + 2) = a.Num

2. 通過

   # Write your MySQL query statement below
   SELECT DISTINCT(a.Num) AS ConsecutiveNums
   FROM Logs AS a
   JOIN Logs AS b
   ON a.Id = b.Id - 1
   JOIN Logs AS c
   ON b.Id = c.Id - 1
   WHERE a.Num = b.Num
   AND b.Num = c.Num