Calculate difference between values with MySQL (PV)

Question

I'm a bit stuck at my Bachelor's thesis and hope you can help me. In order to evaluate a photovoltaic system I need to calculate the difference between total energy amounts. These are automatically updated in a MySQL-table with a timestamp, but without an id-number. I need to get the delta/difference between those energy amounts automatically as a extra column to visualize it in Grafana.

******************************************
Timestamp            | SB1_AC_Total       | Needed information (delta)
******************************************
2020-06-24 09:32:45  | 11.326.302         |   23

2020-06-24 09:32:02  | 11.326.279         |   22

2020-06-24 09:31:20  | 11.326.257         |   ...

This list goes on for weeks. I really hope you can help me, because I have no idea and it is the first time I work with MySQL.

Answer 1

I was able to answer my question with the following code:

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ALTER TABLE TABLENAME  ADD SB1_AC_GES_DIFF INT;
DELIMITER $$
CREATE TRIGGER TABLENAME_Trigger
    BEFORE INSERT
    ON TABLENAME FOR EACH ROW
BEGIN
   DECLARE SB1_AC_GES_old INT;  
  SELECT max(SB1_AC_GES) INTO SB1_AC_GES_old FROM TABLENAME;
   SET NEW.SB1_AC_GES_Diff = New.SB1_AC_GES - SB1_AC_GES_old;
END$$    
DELIMITER ;

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