mysql过程检查条目是否存在

Question

i need a procedure to tell me if a entry exists so i know if i have permission.

    CREATE DEFINER=`root`@`localhost` procedure `checkPermission`(tbl varchar(50), id int, userid int, out b boolean)
begin
    set @q = concat("select idtblUsers into @rs from ", tbl, " where id", tbl, '=', id, ' && idtblUsers=', userid);

    prepare stmt1 FROM @q;
    EXECUTE stmt1;
    DEALLOCATE PREPARE stmt1;

    if @rs is not null then
        select true into b;
    else
        select false into b;
    end if;

END$$

call checkPermission('tblProjects', 2, 1, @b)

it always returns 1 in mysql-workbench even though it says there is no data (warning 1329) if there isn't a entry (i haven't got permission). but i would like true or false back in @b.

Answer 1

Please have a try with this shortened version. The main problem is the DEFINER=root@localhost . This executes the procedure with the rights that root@localhost has. Since he most likely has every right there is, he won't run into permission restrictions. So either you remove it and create the procedure with a restricted user, or you change it to DEFINER=restricted_user@host .
exists() is also the better alternative, since it stops as soon as an entry was found.

CREATE procedure `checkPermission`(tbl varchar(50), id int, userid int, out b boolean)
begin
    set @q = concat("select exists(select 'whatever' into b from ", tbl, " where id", tbl, '=', id, ' && idtblUsers=', userid, ')');

    prepare stmt1 FROM @q;
    EXECUTE stmt1;
    DEALLOCATE PREPARE stmt1;

END$$

Answer 2

it nearly done the job but here is what works for me

CREATE procedure `checkPermission`(tbl varchar(50), id int, userid int, out b boolean) 
begin
    set @q = concat("select exists( select idtblUsers from ", tbl, " where id", tbl, '=', id, ' && idtblUsers=', userid, ') into @b ');

    prepare stmt1 FROM @q;
    EXECUTE stmt1;
    DEALLOCATE PREPARE stmt1;

    select @b into b;
END$$