如果仅选择一个过滤器，则过滤

I have to make a car website that filters cars depending on a preset mysql database. I have got it to filter if all are selected (eg: Honda, white, petrol and not on special - it will show that car) but if I just wanted to see all the Honda's (for example) nothing shows.

This is the code I have:

if(isset($_GET['make']) || isset($_GET['colour']) || isset($_GET['fueltype']) ||          isset($_GET['special'])){

if(isset($_GET['make'])){
$make = $_GET['make'];
}

if(isset($_GET['colour'])){
$colour = $_GET['colour'];
}

if(isset($_GET['fueltype'])){
$fueltype = $_GET['fueltype'];
}

if(isset($_GET['special'])){
$special = $_GET['special'];
}

$result = mysqli_query($con,"SELECT * FROM Cars WHERE MAKE ='$make' AND COLOUR = '$colour' AND FUELTYPE = '$fueltype' AND SPECIAL = '$special'");
}



else{
$result = mysqli_query($con,"SELECT * FROM Cars");
}

the else statement makes all the cars show up when you open the page before filtering.

escape can mean: mysql_escape_string, check against a list of valid/allowed values, or whatever you want after good thinking.

$where = "";
$separator = " WHERE ";

if(isset($_GET['make'])){
    $make = $_GET['make'];
    !! escape here
    $where .= $separator . " MAKE = '$make' ";
    $separator = " AND ";
}

if(isset($_GET['colour'])){
    $colour = $_GET['colour'];
    !! escape here
    $where .= $separator . " COLOUR = '$colour' ";
    $separator = " AND ";
}

... 

$result = mysqli_query($con,"SELECT * FROM Cars " . $where);

Here is how you can do it. Please do something for sql injection attacks. This is only example.

$query  =   "SELECT * FROM Cars ";
$where  =   array();

if(isset($_GET['make'])){
    $where['make'] = $_GET['make'];
}

if(isset($_GET['colour'])){
    $where['colour'] = $_GET['colour'];
}

if(isset($_GET['fueltype'])){
    $where['fueltype'] = $_GET['fueltype'];
}

if(isset($_GET['special'])){
    $where['special'] = $_GET['special'];
}

$string =   '';
if(count($where)>0){
    $i=0;
    foreach($where as $key => $value)
    {
        if($i==0){
            $string .=  " WHERE $key = $value ";
        }else{
            $string .=  " AND $key = $value ";
        }
    $i++;   
    }
}
$query  .=  $string;

mysqli_query($query);

if(isset($_GET['make']) || isset($_GET['colour']) || isset($_GET['fueltype']) ||          isset($_GET['special'])){
$where="WHERE ";
if(isset($_GET['make'])){
$make = $_GET['make'];
$where .="MAKE ='$make' AND";
}

if(isset($_GET['colour'])){
$colour = $_GET['colour'];
$where .="COLOUR = '$colour' AND";
}

if(isset($_GET['fueltype'])){
$fueltype = $_GET['fueltype'];
$where .="FUELTYPE = '$fueltype' AND";
}

if(isset($_GET['special'])){
$special = $_GET['special'];
$where .="SPECIAL = '$special";
}
$where=rtrim($where,'AND');

$result = mysqli_query($con,"SELECT * FROM Cars".$where);
}



else{
$result = mysqli_query($con,"SELECT * FROM Cars");
}

Ignoring the security issues you could replace your whole code with something like this:

$query = "SELECT * FROM Cars WHERE 1 = 1";

if (isset($_GET['make']))
    $query .= ' AND MAKE = ' . (int) $_GET['make'];

if (isset($_GET['colour']))
    $query .= ' AND COLOUR = ' . (int) $_GET['colour'];

if (isset($_GET['fueltype']))
    $query .= ' AND FUELTYPE = ' . (int) $_GET['fueltype'];

if (isset($_GET['special']))
    $query .= ' AND SPECIAL = ' . (int) $_GET['special'];

$result = mysqli_query($con, $query);