mysql user variable assignement with count(*)

Question

I try to do query with a user variable, but I don\'t understand why, i can\'t update the variable in the query. I want to sum the grouped result for each day to do a chart. That

Answer 1

As @JagaSrik said, there is a need to more information about your data and tables to give right answer. However, if you need to change a table like this:

name                |     date      |  id
-----------------------------------------
total Inscription   |   2017-07-10  |   2
total Inscription   |   2020-04-20  |   2
total Inscription   |   2020-04-21  |   3
total Inscription   |   2020-06-17  |   4
total Inscription   |   2020-06-18  |   2

to something like this:

     date      |  total
-----------------------------------------
   2017-07-10  |   2
   2020-04-20  |   4
   2020-04-21  |   7
   2020-06-17  |   11
   2020-06-18  |   13

you can use CURSOR.

For this example:

DELIMITER $$
CREATE PROCEDURE `countIds`()
BEGIN
    DECLARE finished INTEGER DEFAULT 0;
    DECLARE total INTEGER DEFAULT 0;
    DECLARE theCount INTEGER DEFAULT 0;
    DECLARE theDate varchar(100) DEFAULT "";    

        DEClARE curCount 
        CURSOR FOR 
            SELECT `id`,`date` FROM table1;

        DECLARE CONTINUE HANDLER 
    FOR NOT FOUND SET finished = 1;
        
    OPEN curCount;

    getCount: LOOP
        FETCH curCount INTO theCcount,theDate;
        IF finished = 1 THEN 
            LEAVE getCount;
        END IF;
        SET total = total + theCount;
        select theDate, total;
    END LOOP getCount;
    CLOSE curCount;       

END$$
DELIMITER ;

Nevertheless CURSOR is a way to do your work and there may be more effective methods.