How to combine single row with array of data in prepared statements - php

Question

I have two table ad_post and ad_img . One ad_post row has many images in ad_img. I am trying to execute 2 queries together and than combine at the end. but
table:ad_images
colums (img_id, ad_id, img_name)
table : ad_post
colums(id, user_id, title, price, cat, condit, description, vid)
Relationship
ad_post (1)------>(many)ad_images
public function read_ads()
{
$this;
$this->sql = 'SELECT ad_post.id,ad_post.user_id,ad_post.title,ad_post.price,
sub_cat.s_cat_name,ad_post.condit,ad_post.description,ad_post.vid FROM ad_post,sub_cat
where sub_cat.id=ad_post.cat';
$sql1 = 'SELECT `img_id`,`img_name` FROM `ad_images` WHERE ad_id=?';
$stmt = $this->con->prepare ( $this->sql );
$stmt1 = $this->con->prepare ( $sql1 );
if ($stmt === false) {
trigger_error ( 'Wrong SQL: ' . $sql . ' Error: ' . $conn->error, E_USER_ERROR );
}
// STMT
$stmt->execute ();
$stmt->store_result ();
$stmt->bind_result ( $id, $uId, $title, $price, $cat, $usage, $desc, $vid );
// STMT1
// $ad =AdPost::__getAll('','','','','','','','');
// $ad = Array();
$img = Array ();
$count = 0;
$count = 0;
$ads_img = Array ();
$a_img = Array ();
while ( $stmt->fetch () != NULL ) {
$stmt1->bind_param ( 'i', $id );
$stmt1->execute ();
$stmt1->store_result ();
$stmt1->bind_result ( $img_id, $img_name );
while ( $stmt1->fetch () != NULL ) {
echo $img_id;
$a_img = Array (
'img_id' => $img_id,
'img_name' => $img_name
);
try {
$ads_img [$count] = $a_img;
} catch ( Exception $exc ) {
echo $exc->getTraceAsString ();
}
}
$count ++;
$ad_set = Array (
'id' => $id,
'uid' => $uId,
'title' => $title,
'price' => $price,
'cat' => $cat,
'usage' => $usage,
'desc' => $desc,
'img_name' => $a_img
);
try {
$ads [$count] = $ad_set;
} catch ( Exception $exc ) {
echo $exc->getTraceAsString ();
}
$count ++;
}
$stmt->free_result ();
$stmt->close ();
return $ads;
}
I have got the ids of ads now i want to save imgs in array of $ad_set
The values of image array are returning null