Místo těchto proměnných byste měli použít operátor ".=".
/* $t1 = '';
$t2 = '';
$t3 = '';
$t4 = '';
$t5 = '';
*/
$q = "SELECT * FROM `property` WHERE `status`='1' ";
// You need to enclose all **OR** logical tests in parenthesis.
// Moreover most of the usages of isset function are useless,
// as your are initializing many variables
if($keyword && !empty($keyword)){
$q .= " AND (`p_title` LIKE '%".$keyword."%' OR `address` LIKE '%".$keyword."%' OR `area` LIKE '%".$keyword."%')";
}
if($prop_for && !empty($prop_for)){
// If you are using double quotes you really don't need handle to concatenation.
$q .= " AND `p_for`='$prop_for'";
}
if($state && !empty($state)){
$q .= " AND `state`='$state'";
}
if($ptype && !empty($ptype)){
$q .= " AND `p_category`='$ptype'";
}
//min only
if($min_price && !empty($min_price)){
$q .= " AND `price` >= '".$min_price."'";
}
//max only
if($max_price && !empty($max_price)){
$q .= " AND `price` <= '$max_price'";
}
// When you are not using OFFSET keyword,
//the first number after LIMIT keyword should be the number of records
$q .= " ORDER BY `posted_date` DESC LIMIT $per_page , $start;";
$sql = $mysqli->query($q);