प्रति समूह एन यादृच्छिक रिकॉर्ड का चयन करें

मैंने तबेला और कैंपो मापदंडों को प्रक्रिया से हटा दिया ताकि इसे समझना आसान हो सके। मुझे यकीन है कि आप उन्हें वापस ला सकते हैं।

delimiter //
drop procedure if exists casualiPerGruppo //
create procedure casualiPerGruppo(in numPerGruppo int)
begin
declare valore int;
declare finite int default 0;
declare query_part varchar(200);
declare query_union varchar(2000);
declare cur_gruppi cursor for select distinct id_gruppo from prova;
declare continue handler for not found set finite = 1;

create temporary table resultset (id int, id_gruppo int, altro varchar(10));

set @query_part = 'select id, id_gruppo, altro from (select id, id_gruppo, altro from prova where id_gruppo = @id_gruppo order by rand() limit @numPerGruppo) [email protected]_gruppo';
set @query_part = replace(@query_part, '@numPerGruppo', numPerGruppo);
set @query_union = '';

open cur_gruppi;
mio_loop:loop
fetch cur_gruppi into valore;
    if finite = 1 then
        leave mio_loop;
    end if;

set @query_union = concat(@query_union, concat(' union ', @query_part));
set @query_union = replace(@query_union, '@id_gruppo', valore);

end loop;
close cur_gruppi;

set @query_union = substr(@query_union, 8);
set @query_union = concat('insert into resultset ', @query_union);

prepare stmt from @query_union;
execute stmt;
deallocate prepare stmt;
select * from resultset order by id_gruppo, altro;
drop table resultset;

end //
delimiter ;