在php中，执行以下操作：

// Initalizing query string
$sql = "SELECT * FROM table ";

// Preparing where conditions
$whr = array();
if (!empty($first_name)) {
    $whr[] = "first_name = '" . real_escape_string($first_name) . "'";
} 

/* Like this check for other variables/fields */

// Adding where statement
if (!empty($whr)) {
    $sql .= " WHERE ";
    $sql .= implode(' AND ', $whr);
}

// Now execute the query and fetch results