MySQL difference between two rows of a SELECT Statement

Question

I am trying to make the difference of two rows in an mysql database.
I have this table containing ID, kilometers, date, car_id, car_driver etc...
Since I don\'t alwa

Answer 1

With MySQL 8 you can use CTE and ROW_NUMBER window function to make a more readable query

WITH cte_name AS (
    SELECT
    ROW_NUMBER() OVER (ORDER BY update_time) as row_num,
    id,
    other_data,
    update_time
    FROM table_name WHERE condition = 'some_condition'
)
SELECT t2.id, t2.other_data, TIMEDIFF(t2.update_time, t1.update_time) AS time_taken
FROM
cte_name t1
JOIN cte_name t2 ON t1.row_num = t2.row_num-1
ORDER BY time_taken;

In this example I'm trying get the difference between datetime values.

• The idea is to use ROW_NUMBER window function to assign an incremental number to each row after ordering by update_time.
• The CTE allows us to write a subquery without having to repeat writing the same code.
• We self join the CTE. The joining condition is basically - each nᵗʰ item of the second subquery joins with the n-1ᵗʰ item of the first subquery (this also means the first row will disappear from the result set. if you need it you can use a UNION to add the first row to the start).

There are some good tutorials for: CTE (Common Table Expression), ROW_NUMBER and even window functions