How to make a query to the database?

Question

MySQL

There are search parameters in GET for a database request:
search.php?lic=0&section=1,2&type=1,2,3,4
One of the 3 parameters will be mandatory, but any other two may not be. How to query the database?
For example I do this:

SELECT `id`
FROM `content`
WHERE lic='".$lic."' AND section='".$section."' AND type='".$type."'

But if one of the lic or section or type variables is empty, will the query work with an empty condition?

Answer 1

What are variables equal to if they are not present in the query? If the value is an empty string, then you can write it like this:

$req = $mysqli->prepare(
    "SELECT `id` FROM `content` ".
        "WHERE ('' = ? OR `lic` = ?) ".
            "AND ('' = ? OR `selection` = ?) ".
            "AND ('' = ? OR `type` = ?)"
);
$req->bind_param('ssssss', $lic, $lic, $selection, $selection, $type, $type);

Answer 2

Instead of AND, write OR and try.

Answer 3

In addition to the answers above, do not only check, but also intval functions - if you're expecting a number, strip_tags. Better yet, use PDO.