If data = 0 then do not update(execute) table. (JavaScript/SQL)
<p>I only want the update query to be executed if the "VacantSpaces" is not 0. So in other words, once there is no longer any spaces for a specific event "VacantSpaces" will be 0 so the idea is that users should not be able to join and the number will not go -1, -2 etc. </p>

<p>However I am not quite sure how to go about this.</p>

<p>JavaScript Function:</p>

<pre><code>function updateEvent(title) {
    db = window.openDatabase("SoccerEarth", "2.0", "SoccerEarthDB", 2 * 1024 * 1024);
    db.transaction(function(tx) {
        tx.executeSql("Update EventSoccer SET VacantSpaces = VacantSpaces -1, NoPeople = NoPeople + 1 
                       WHERE Title = '" + title + "'", 
                       [], 
                       successJoin,
                       errorCB
        );
    });

    function successJoin() {
        navigator.notification.alert("You have joined the event!",
                                      null, 
                                      "Information", "ok");

        $( ":mobile-pagecontainer" ).pagecontainer( "change", "#page4" );
    }
}
</code></pre>