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 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;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 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。
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