Arithmetic operation in MySQL through Procedure - mysql

Question

I have a table t1 which have a column Marks in this column values are 10, 20, 30, 40.
Now I want to use a procedure to get this result:
Marks Total_Marks
10 10
20 30
30 60
40 100
DELIMITER //
CREATE PROCEDURE Total_Marks ( In Num Int(4) )
Begin
Declare Mark Int(4);
Declare Add_M Int(4);
DECLARE NO_MORE_ROWS BOOLEAN;
DECLARE DataCursor CURSOR FOR SELECT Marks
FROM t1 where marks = Num;
DECLARE DataCursor1 CURSOR FOR SELECT Sum(Marks) FROM t1;
OPEN DataCursor;
FETCH DataCursor INTO Mark;
CLOSE DataCursor;
OPEN DataCursor1;
READ_LOOP1: LOOP
FETCH DataCursor1 INTO Add_M;
IF NO_MORE_ROWS THEN
LEAVE READ_LOOP1;
END IF;
BEGIN
SET Add_M = SUM(Mark);
END;
END LOOP READ_LOOP1;
CLOSE dataCursor1;
SET NO_MORE_ROWS = FALSE;
end //
DELIMITER ;

Answer 1

You don't need a procedure at all, let alone cursors. But what you need, is a column that defines the order of the rows as mentioned in the comments.
create table foo (id int auto_increment primary key, bar int);
insert into foo(bar) values (10), (20), (30), (40);
In this example I introduced the column id for that matter. Or you can of course just order by your marks or whatever suits your needs.
select
bar
, #total := #total + bar as my_total
from
foo
, (select #total := 0) var_init
order by id
see it working live in this sqlfiddle
As explanation, with this cross joined query
, (select #total := 0) var_init
we initialize our variable holding the running total #total. It's the same as writing
set #total = 0;
select
bar
, #total := #total + bar as my_total
from
foo
order by id;
The rest is self explaining I guess.
You can read more about these type of variables here.
UPDATE (for completeness):
Here are two other possibilities how to solve it without variables. Although I like variables usually better, cause in this one
select
t1.bar
, sum(t2.bar)
from
foo t1
inner join foo t2 on t1.id >= t2.id
group by t1.id;
you end up with a potentially huge temporary table, since you join every row to all previous rows and then calculate the sum.
And in this solution
select
bar
, (select sum(bar) from foo sf where sf.id <= foo.id) as my_total
from
foo;
you have a dependent subquery executed for each row. This is even worse than the previous solution.
I posted those just for completeness and if you really can't use variables (because of creating a view for example).