PHP advanced search function

[dmmh]

I'm trying to write an advanced filter function.
Sofar I have 5 parameters which could lead to 25 possible queries. Instead of having to write them all, how do people normally tackle this problem?

[Mr_Fern]

The method I use is setting up an array for all the different possible search options. Hope this helps any.

$where = array();

//do this for each form field

if ($_POST['field1']!= "")
$where[] = "databaseColumn = '$_POST[field1]'";
...
if ($_POST['fieldN']!= "")
$where[] = "databaseColumn = '$_POST[fieldN]'";

$where_size = count($where);

for ($i = 0;$i < $where_size; $i++)
$q_where .= "$where[$i] OR ";

$q_where = substr($q_where,0,-4); // remove the last " OR ";

$sql = "SELECT [columns] FROM [table] WHERE $q_where ORDER BY [columnName] LIMIT [number]";

[dmmh]

nice, thank you very much

[dmmh]

well, I am almost there. I made a page where people can select categories and other variables to display a list of matching files.

the query is quite ok if people only select one category, but they are allowed to search multiple. If they specify an operator and a language and one category, only rows containing the specified language and operator will be returned. If they specify more then one category, they query fails. Well it doesnt fail, but it returns rows with languages other then the ones specified. I can see why it fails, but I cant figure out a way to sort it properly.
So, all variables except the catgory_id one are limited to one value, while the category_id may be an array

My code:

$device_id = mysql_real_escape_string($_GET['device_id']);
$operator_id = mysql_real_escape_string($_GET['operator_id']);
$country_id = mysql_real_escape_string($_GET['country_id']);
$language_id = mysql_real_escape_string($_GET['language_id']);
$category_id = $_GET['category_id'];
//$cats_arr_asigned = split(",", $row['categories']);
$nr_categories_get = count($_GET['category_id']);

if (!empty($device_id)){
if (!empty($operator_id)){
$query_part2 = " AND files.operator = '$operator_id'";
}
if (!empty($country_id)){
$query_part3 = " AND files.country = '$country_id'";
}
if (!empty($language_id)){
$query_part4 = " AND files.language = '$language_id'";
}
if (!empty($category_id)){
for($i=0; $i<$nr_categories_get; $i++){
$category_id_new = mysql_real_escape_string($category_id[$i]);
if ($i==0){$start = ' AND';}else{$start = ' OR';}
$query_part_tmp .= $start;
$query_part_tmp .= " FIND_IN_SET('$category_id_new', files.categories)";
}
$query_part5 = $query_part_tmp;
}
@mysql_select_db('db');
$query = 'SELECT * FROM files'.
" WHERE device_id = '$device_id' $query_part2 $query_part3 $query_part4 $query_part5 ORDER BY files.filename";

I know the error lies here:
if ($i==0){$start = ' AND';}else{$start = ' OR';}

but I dont know how to fix it, so any help would be appreciated