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               |
+-----------------+

題意:求表中連續出現3次以上的數據.

因此，根據題意構造第一版本答案（使用連續的ID進行比較）:

# Write your MySQL query statement below
SELECT 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;

當前版本答案通過了測試，但是運行效率太低了.
分析原因，可能與t1.Id = t3.Id - 1條件相關，當t3.Id為0時，-1不會尋找到相關數據，導致sql執行緩慢.
因此，修改為如下所示：

# Write your MySQL query statement below
# Write your MySQL query statement below
SELECT 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。