180 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.

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 

三張表自己連接，根據ID的連續(xù)性找到連續(xù)出現(xiàn)的數(shù)字。
找出這些數(shù)字以后再使用 DISTINCT 關鍵字去重一下。