指定的表不存在[,,,,,]

Question

private string connectionString = @"Provider=Microsoft.SQLSERVER.CE.OLEDB.4.0;" + @"Data Source=..\\..\\..\\MusicDatabase.sdf";

try
{
    DataTable table = new DataTable();
    string command = getcommand.CheckuserName(usernametb);
    MessageBox.Show(command);
    OleDbDataAdapter adapter = new OleDbDataAdapter(command, connectionString);

    // do the query
    table.Clear();
    int recordCount = adapter.Fill(table); // Error

    // display results
    if (recordCount != 0)
    {
       MessageBox.Show("Username not available!");
    }
    else
    {
    }
}
catch (Exception obj)
{
    MessageBox.Show(obj.ToString());
}

给我错误：指定的表格不存在[,,,,,] 我尝试了很多东西，但它不起作用。 getcommand.CheckuserName(usernametb);

返回：

    public string CheckuserName(string usernametb)
    {
        string command = "SELECT * FROM USERS WHERE " +
                              "username = '" + usernametb + "'";
        return command;
    }

所以它返回：

    SELECT * FROM USERS WHERE username = 'name'