Select all users with specific MySql request PHP

Question

I'm coding a feature in PHP, it's a search engine.

 <form action="result" method="POST"> <select name="instrument" id="instrument"> <option value="all">All instrument</option> <option value="1">Guitar</option> <option value="2">Bass</option> <option value="3">Battery</option> <option value="4">Singer</option> </select> <select name="theme" id="theme"> <option value="all">All themes</option> <option value="1">Metal</option> <option value="2">Jazz</option> <option value="3">Rock</option> <option value="4">Blues</option> </select> <input type="submit" value="search" /> </form> 

I already code this search engine like this and it works

<?php 


if(isset($_POST)) {

    $theme = $_POST['theme'];
    $instrument = $_POST['instrument'];


    $req_search = $bdd->query("SELECT * FROM user,theme,instrument WHERE theme.theme_id = user.user_theme AND instrument.instrument_id = user.user_instrument AND theme_id =".$theme." AND instrument_id =".$instrument);

    if($req_search->rowCount()>0) {

    while($search = $req_search->fetch()) {

        ?>

        <p><?php echo $search['user_username']; ?></p>

    <?php 

    }

    $req_search->closeCursor();

    } else {
        echo "Users not found";
    }

}

?>

You can find users who is matching with those options (without All instrument and All themes .

Everything is stored into a MySql database.

However when I click on All themes and All instrument . I want to update my select request. Like if I select All instrument and All themes I want to display every users. Or if I select All instrument and Metal , I want to display all users listening to metal and playing whatever instrument.

Thanks for your help !

Answer 1

You can construct your query to be conditional depending on whether $theme and $instrument have values:

$query = "SELECT * FROM user,theme,instrument 
    WHERE theme.theme_id = user.user_theme
    AND instrument.instrument_id = user.user_instrument".
    ($theme!="" ? " AND theme_id='$theme'" : "").
    ($instrument!="" ? " AND instrument_id='$instrument'" : "");

$req_search = $bdd->query($query);

That said, you should look into PDO Prepared Statements and Placeholders , because all this would take is someone to fiddle around with the DOM to perform some MySQL Injection.