使用PHP和Form使用SQL SELECT Query进行多重排序

Question

I use a html form with 6 criterias, using $_POST lat's convert criterias in variables like here:

Case 1 - All criterias are default
$core = null; $mhz = null; $ram = null; $cam = null; $mAh = null $screen = null
The correct sql query is this :
$sql = "SELECT * FROM $tbl_name ORDER BY performanta_cpu_core DESC, performanta_cpu DESC, performanta_rami DESC LIMIT $start, $limit";

Case 2 - Only one criteria is set
$core = null; $mhz = "performanta_cpu=1400"; $ram = null; $cam = null; $mAh = null $screen = null
The corect query is this :
$sql = "SELECT * FROM $tbl_name WHERE $mhzz ORDER BY performanta_cpu_core DESC, performanta_cpu DESC, performanta_rami DESC LIMIT $start, $limit";

Case 3 - Here is the problem All or more than one criterias ore setted:
$core = 2; $mhz = "performanta_cpu=1400"; $ram = "performanta_rami=1024"; $cam = "camera_spate=3.2"; $mAh = "baterie_mAh=2250"; $screen = "densitate=441";

I understand that i have need to make " WHERE " to be dinamic and visible just when any variable is set and also I have need an " AND " also dinamically like:

$sql = "SELECT * FROM $tbl_name WHERE $core AND $mhzz ORDER BY performanta_cpu_core DESC, performanta_cpu DESC, performanta_rami DESC LIMIT $start, $limit";
I am stressed for a week with this and i cant advance without help...

Thanks in advance

Answer 1

Disclaimer: This is terrible code and there are a million better ways to do this, but, this is the simplest explanation.

$parameters = array();
if(!empty($core)){
$parameters['core'] = $core;
}
if(!empty($mhz)){
$parameters['mhz'] = $mhz;
}
if(!empty($ram)){
$parameters['ram'] = $ram;
}
if(!empty($cam)){
$parameters['cam'] = $cam;
}
if(!empty($mAh)){
$parameters['mAh'] = $mAh;
}
if(!empty($screen)){
$parameters['screen'] = $screen;
}

$sql = "SELECT * FROM $tbl_name WHERE 1=1 ";
foreach($parameters as $k=>$v){
 $sql .= " AND ".$k."='".$v."'";
}
$sql .=  " ORDER BY performanta_cpu_core DESC, performanta_cpu DESC, performanta_rami DESC LIMIT $start, $limit";

// All of those parameters should be sanitized to prevent SQL injection.
// mysql_* is deprecated, use mysqli_* or PDO.

Answer 2

Excellently formatted question.. well done.

I may well be misinterpreting the question, however I think you're asking how to construct a query dynamically. Perhaps you are not aware you concat strings ?

Eg.

if ($core != null) {$query.= 'AND core ='.$core;}

I hope this puts you in the right direction.

Answer 3

Start with the beginning of your query, and to make the command easier to build add an "always true" WHERE condition:

$sql = "SELECT * FROM $tbl_name WHERE 1=1";

Then go through your variables and add to the WHERE condition as needed (the space before the AND is really important):

if ($core) $sql .= " AND performanta_cpu_core = '$core'";
if ($mhz) $sql .= " AND whatever = '$mhz'";
... and so on for the other four variables

Then append your ORDER BY and LIMIT and you're done (the space before the ORDER BY is really important):

$sql .= " ORDER BY performanta_cpu_core DESC, performanta_cpu DESC, performanta_rami DESC LIMIT $start, $limit";

Also, as Mahmut pointed out, you can't have WHERE $mhz , you've got to have WHERE your-column-name = $mhz .

Make sure you try out the query from the MySQL command line or WorkBench first. That will help you with syntax, including which columns need single quotes around them and which ones don't.

This isn't the ideal way to assemble a query but it'll work, and it looks like you're just getting started with PHP/MySQL so no need to throw you too much at once.

Answer 4

$parameters = array();
if(!empty($core)){
    $parameters[] = "core = '$core'";
}
if(!empty($mhz)){
    $parameters[] = "mhz = '$mhz'";
}
if(!empty($ram)){
    $parameters[] = "ran = '$ram'";
}
if(!empty($cam)){
    $parameters[] = "cam = '$cam'";
}
if(!empty($mAh)){
    $parameters[] = "mAh = '$mAh'";
}
if(!empty($screen)){
    $parameters[] = "screen = $screen";
}

if (empty($parameters)) {
   $whereclause = "";
} else {
   $whereclause = "WHERE " . join(' AND ', $parameters);
}

$sql = "SELECT * FROM $tbl_name $whereclause ORDER BY performanta_cpu_core DESC, performanta_cpu DESC, performanta_rami DESC LIMIT $start, $limit";

Answer 5

You can use array_filter and implode to build your where clause

$conditions = array_filter(array($core, $mhz, $ram, $cam, $mAh, $screen));
$clause = implode(' and ', $conditions);

This keeps all non null elements as $conditions and then concatenates these with and . You can then use this as

'... where ' . $clause . '...'