I would like to know if it is possible with MySql/MariaDB to use indexes directly in queries. Let's say we have a simple unsorted table with timestamp/value pairs:

CREATE TABLE simple (timestamp DATETIME, val INT);

Index by adding timestamp:

ALTER TABLE simple ADD INDEX ind_ts (timestamp);

We can "quickly access" some sorted order of timestamps.

Let's define a query to provide the difference in values ​​for consecutive values:

SELECT 
    c.timestamp AS currenttimestamp,
    COALESCE(b.timestamp,'0000-00-00 00:00:00') AS timestampbefore,
    c.val - COALESCE(b.val,0) AS difference
FROM simple c, 
simple b 
WHERE b.timestamp = (SELECT MAX(timestamp) FROM simple h WHERE h.timestamp < c.timestamp)

Obviously, this query is conditional and expensive. A more convenient way is to add the column myindex to the table:

ALTER TABLE simple ADD COLUMN (myindex INT) AFTER timestamp;

and populate the new column with the chronological order of the timestamp (e.g. via some php code)

New queries will be simpler and cheaper:

SELECT 
    c.timestamp AS currenttimestamp,
    COALESCE(b.timestamp,'0000-00-00 00:00:00') AS timestampbefore,
    c.val - COALESCE(b.val,0) AS difference
FROM simple c
LEFT JOIN simple b ON c.myindex = b.myindex+1

The new column myindex is similar to the database table index ind_ts to some extent. (Why) Is there no MySql construct to use ind_ts instead of myindex?