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1285. Find the Start and End Number of Continuous Ranges
Description
Table: Logs
+---------------+---------+ | Column Name | Type | +---------------+---------+ | log_id | int | +---------------+---------+ log_id is the column of unique values for this table. Each row of this table contains the ID in a log Table.
Write a solution to find the start and end number of continuous ranges in the table Logs.
Return the result table ordered by start_id.
The result format is in the following example.
Example 1:
Input: Logs table: +------------+ | log_id | +------------+ | 1 | | 2 | | 3 | | 7 | | 8 | | 10 | +------------+ Output: +------------+--------------+ | start_id | end_id | +------------+--------------+ | 1 | 3 | | 7 | 8 | | 10 | 10 | +------------+--------------+ Explanation: The result table should contain all ranges in table Logs. From 1 to 3 is contained in the table. From 4 to 6 is missing in the table From 7 to 8 is contained in the table. Number 9 is missing from the table. Number 10 is contained in the table.
Solutions
Solution 1: Group By + Window Function
We need to find a way to group a continuous sequence of logs into the same group, and then aggregate each group to obtain the start and end logs of each group.
There are two ways to implement grouping:
- By calculating the difference between each log and the previous log, if the difference is $1$, then the two logs are continuous, and we set $delta$ to $0$, otherwise we set it to $1$. Then we take the prefix sum of $delta$ to obtain the grouping identifier for each row.
- By calculating the difference between the current log and its row number, we obtain the grouping identifier for each row.
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# Write your MySQL query statement below WITH T AS ( SELECT log_id, SUM(delta) OVER (ORDER BY log_id) AS pid FROM ( SELECT log_id, IF((log_id - LAG(log_id) OVER (ORDER BY log_id)) = 1, 0, 1) AS delta FROM Logs ) AS t ) SELECT MIN(log_id) AS start_id, MAX(log_id) AS end_id FROM T GROUP BY pid;