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.

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

sql脚本

SELECT DISTINCT L1.Num as ConsecutiveNumsFROM Logs L1, Logs L2, Logs L3WHERE L2.Id = L1.Id + 1AND L3.Id = L2.Id + 1AND L1.Num = L2.NumAND L2.Num = L3.Num

也可以使用JOIN子句完成同样的功能：

SELECT DISTINCT L1.Num FROM Logs L1JOIN Logs L2 ON L1.Id + 1 = L2.IdJOIN Logs L3 ON L1.Id + 2 = L3.IdWHERE L1.Num = L2.Num AND L1.Num = L3.NumORDER BY L1.Num

上面两种方法可以用于找到至少三次连续出现的数字，如果将连续出现的数字扩展到N个，按照上面思路写出的SQL语句就会比较长。因此可以用下面这种方式来查询：

SELECT DISTINCT NumFROM (  SELECT Num,     CASE       WHEN @prev = Num THEN @count := @count + 1      WHEN (@prev := Num) IS NOT NULL THEN @count := 1    END CNT  FROM Logs, (SELECT @prev := NULL) X  ORDER BY Id) AS AWHERE A.CNT >= 3

将最后一行的3改为N，即可用于查询至少N次连续出现的数字。