If a $request body was passed in with the categories 9,1,7 and I try to do the following it only will return the categories with ID 9

        $categories = implode('","',$request->categories);

        $statement = <<<'ENDSTATEMENT'
        SELECT 
            locations.name,
            locations.id,
            locations.lon,
            locations.lat,
            locations_categories.category_id as catId,
            locations_categories.location_id as locId,
            haversine(?,?,locations.lon,locations.lat) as distance
        FROM locations_categories, locations  
        WHERE locations.id = locations_categories.location_id
        AND locations_categories.category_id IN (?)  
        ORDER BY `distance` ASC
ENDSTATEMENT;

    $locations = DB::select($statement, array($request->lon, $request->lat, $categories));

But if if I was to do

AND locations_categories.category_id IN ("9","1","7")

Instead of passing the $categories variable in it returns all of the categories.

Why would it work for the hard coding but not passing the parameters in?