关于java：从mysql网站检索时未选择数据库

No Database selected when retrieving from mysql website

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，但是它告诉我：

1	java.sql.SQLException: No database selected

码：

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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：

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

任何人都有什么想法会导致这样的事情？