When I create the saved procedure, i can create some variable yes? for example:
CREATE PROCEDURE `some_proc` ()
BEGIN
DECLARE some_var INT;
SET some_var = 3;
....
DECLARE some_var INT;
SET some_var = SELECT COUNT(*) FROM mytable ;
There are multiple ways to do this.
You can use a subquery:
SET some_var = (SELECT COUNT(*) FROM mytable);
(like your original, just add parenthesis around the query)
or use the SELECT INTO syntax to assign multiple values:
SELECT COUNT(*), MAX(col)
INTO some_var, some_other_var
FROM tab;
The subquery syntax is slightly faster (I don't know why) but only works to assign a single value. The select into syntax allows you to set multiple values at once, so if you need to grab multiple values from the query you should do that rather than execute the query again and again for each variable.
Finally, if your query returns not a single row but a resultset, you can use a cursor.