Leetcode SQL

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

Logic:

Create three temp tables and then compare them accordingly. Remember to use Distinct(). Also, I have to use A=B and B=C, instead of A=B=C in SQL.

Solution:

select distinct(l1.Num) as ConsecutiveNums from Logs l1, Logs l2, Logs l3
where l1.Num = l2.Num and l2.Num = l3.Num
and l1.Id = l2.Id-1 and l2.Id = l3.Id-1;

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