I'm creating a large PHP project and I've a trivial doubt about how to proceed.

Assume we got a class books, in this class I've the method ReturnInfo:

function ReturnInfo($id) {
    if( is_numeric($id) ) {
        $query = "SELECT * FROM books WHERE id='" . $id . "' LIMIT 1;";

        if( $row = $this->DBDrive->ExecuteQuery($query, $FetchResults=TRUE) )   {  
                return $row;
        } else {
            return FALSE;
        }
    } else {
        throw new Exception('Books - ReturnInfo - id not valid.');          
    }
}

Then i have another method PrintInfo

function PrintInfo($id) {
    print_r( $this->ReturnInfo($id) );
}

Obviously the code sample are just for example and not actual production code.

In the second method should I check (again) if id is numeric ? Or can I skip it because is already taken care in the first method and if it's not an exception will be thrown?

Till now I always wrote code with redundant checks (no matter if already checked elsewhere i'll check it also here)

Is there a best practice? Is just common sense?

Thank you in advance for your kind replies.