How to speed up stored procedure in mysql - mysql

Question

Below given is my procedure takes too much time to execute.
BEGIN
DECLARE rank1 BIGINT DEFAULT 0;
DECLARE id1 BIGINT;
DECLARE rankskip BIGINT DEFAULT 0;
DECLARE mark DECIMAL(10,2) DEFAULT 0;
DECLARE oldmark DECIMAL(10,2) DEFAULT -100000;
DECLARE done int DEFAULT 0;
DECLARE cursor_i CURSOR FOR
SELECT
(rightmarks - negativemarks) as mark, id
FROM
testresult
WHERE
testid = testid1
ORDER BY
(rightmarks - negativemarks) DESC;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;
OPEN cursor_i;
read_loop: LOOP
FETCH cursor_i INTO mark, id1;
IF done = 1 THEN
LEAVE read_loop;
END IF;
IF oldmark = mark THEN
BEGIN
IF IsRankSkip = 1 THEN
BEGIN
SET rankskip = rankskip + 1;
END;
END IF;
END;
ELSE
BEGIN
SET rank1 = rank1 + rankskip + 1;
SET rankskip = 0;
END;
END IF;
SET oldmark = mark;
UPDATE testresult SET rank = rank1 WHERE id=id1;
END LOOP;
CLOSE cursor_i;
END
This loop iterate minimum 2000 times.
Here IsRankSkip and testid1 is an argument passed to the procedure.
This procedure takes 65.343152046204 time to execute. If anybody guide me how can I reduce executing time?
Thank you in advance.

Answer 1

You can do this with a single update statement, making use of variables that change during the execution of it:
UPDATE testresult a
JOIN ( SELECT id,
#row := #row + 1 row_number,
#rank := if(mark = #lastmark, #rank, #row) as rank,
#dense_rank := #dense_rank + if(mark = #lastmark, 0, 1) as dense_rank,
#lastmark := mark as mark
FROM ( SELECT rightmarks - negativemarks as mark,
id
FROM testresult
WHERE testid = testid1
ORDER BY 1 DESC
) data,
(SELECT #row := 0, #dense_rank := 0) r
) b
ON a.id = b.id
SET a.rank = if(IsRankSkip, b.rank, b.dense_rank);
The query with alias b calculates the rank and adds it as a column in the result set. In fact, it adds three kinds of numbers:
#row: the sequential row number without special treatment of equal values
#rank: the same as row number of the value differs from the previous value, otherwise it is the same as in the previous row
#dense_rank: this increments when the value differs from the previous value, otherwise it is the same as in the previous row
You can choose which one to update your rank column with. In the above SQL I have used the two procedure variables IsRankSkip and testid1.
Remark
If you are always calling your procedure for all testid values, then the above can be further improved, so all these updates are done with only one update statement.