mysql select table from anther table from $_GET - mysql

Question

I need to select id from sub where mainid = $cccc as iiid and after that select from ads where cat = iiid
and select order from ads order by id desc limit 10
$cccc=intval($_GET['cat']);
$DB = new DB;
$seleddcddddtMainwork ="select id from sub where mainid='$cccc' as iiid from ads where cat='$idididid' order by id desc limit 10 ";
I tried many codes with that but it's not work with me.
I tried:
select sub.mainid='$cccc' as idididid from ads where cat='$idididid' order by id desc limit 10
but I need to get id from sub where mainid=cccc and ahter that select from ads where cat = that id
CREATE TABLE IF NOT EXISTS `ads` (
`id` int(255) NOT NULL AUTO_INCREMENT,
`userid` int(255) NOT NULL,
`title` varchar(255) NOT NULL,
`photo` varchar(255) NOT NULL,
`message` varchar(255) NOT NULL,
`price` int(255) NOT NULL,
`contery` varchar(255) NOT NULL,
`mobile` varchar(255) NOT NULL,
`showmobile` int(255) NOT NULL,
`showj` int(255) NOT NULL DEFAULT '0',
`youtuube` varchar(255) NOT NULL,
`cat` int(255) NOT NULL,
PRIMARY KEY (`id`),
KEY `photo` (`photo`),
KEY `title` (`title`),
KEY `message` (`message`),
KEY `price` (`price`),
KEY `contery` (`contery`),
KEY `mobile` (`mobile`),
KEY `showmobile` (`showmobile`),
KEY `show` (`showj`),
KEY `youtuube` (`youtuube`),
KEY `userid` (`userid`),
KEY `cat` (`cat`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=2 ;
CREATE TABLE IF NOT EXISTS `sub` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(255) NOT NULL,
`mainid` int(255) NOT NULL,
PRIMARY KEY (`id`),
KEY `name` (`name`),
KEY `mainid` (`mainid`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=126 ;
My last try was:
select id from sub.mainid='$cccc' as idididid from ads where cat='idididid' order by id desc limit 10
did not work either.
All I have one value $cccc=intval($_GET['cat']); that I need to select id from sub where mainid=$cccc as iit and select from ads where cat=iit
Another thing
SELECT sub.id, sub.mainid
FROM sub
WHERE sub.mainid = '2'
and
result of this sub.id result from ads where cat = sub.id

Answer 1

Why dont you do a join? If you want to select the id from table #1 in table #2, then you should join the two tables by the id value:
$cccc=intval($_GET['cat']);
$DB = new DB;
$seleddcddddtMainwork ="select S.id from sub S JOIN ads A ON S.mainid=A.id AND C.cat='$idididid' AND S.mainid='$cccc' order by S.id desc limit 10";
Make sure you select all the columns you need. In the query above, only the column id from the sub table is being selected:
select S.id from ....
To select the columns id, name and mainid from sub and the field message and price from ads:
$cccc=intval($_GET['cat']);
$DB = new DB;
$seleddcddddtMainwork ="select S.id, S.name, S.mainid, A.message, A.price from sub S JOIN ads A ON S.id=A.mainidAND C.cat='$idididid' AND S.mainid='$cccc' order by S.id desc limit 10";
Edit:
I changed the JOIN ON 'S.id=A.id' to 'S.id=A.mainid' I believe those are the ids you want to join.
In response to your comment:
all i have one value $cccc=intval($_GET['cat']); that i need to select
id from sub where mainid=$cccc as iit and select from ads where
cat=iit
You can do the following:
$cccc=intval($_GET['cat']);
$DB = new DB;
$seleddcddddtMainwork ="select S.id, S.name, S.mainid as iit, A.message, A.price from sub S JOIN ads A ON S.mainid=A.cat AND S.mainid='$cccc' order by A.id desc limit 10";