我有一个mysql数据库，正试图从我们的网站主机（godaddy）中检索。我遵循的格式似乎正确，但它告诉我：

java.sql.SQLException: No database selected

码：

public static void main(String[] args) {

    Connection conn = null;
    Statement stmt = null;

    try {
        // STEP 2: Register JDBC driver
        Class.forName(JDBC_DRIVER);

        // STEP 3: Open a connection
        System.out.println("Connecting to database...");
        conn = DriverManager.getConnection(DB_URL, USER, PASS);

        // STEP 4: Execute a query
        System.out.println("Creating statement...");
        stmt = conn.createStatement();
        String sql;
        sql = "SELECT * FROM item_master";
        ResultSet rs = stmt.executeQuery(sql);  //<-- This is where the error is.

        // STEP 5: Extract data from result set
        while (rs.next()) {
            // Retrieve by column name
            int id = rs.getInt("id");

            // Display values
            System.out.print("ID: " + id);
        }
...
}

我做了conn的print语句，以为连接可能为空，并显示为：

com.mysql.jdbc.JDBC4Connection@2a6*****

任何人都有什么想法会导致这样的事情？