我试图检查，如果一个特定的值已经存在于我的数据库中。谁能告诉我，我的陈述有什么问题吗？而且我不能将数据插入mysql。谢谢

try {                      
               Statement s = c.createStatement();
             final String queryCheck = "SELECT COUNT(*)FROM pengguna WHERE pengguna.username = '"+ username +"'";
final PreparedStatement ps = c.prepareStatement(queryCheck);
ps.setString(1, username);
final ResultSet resultSet = ps.executeQuery();
if(resultSet.next()) {
  final int count = resultSet.getInt(1);
}
else{
                this.sql = "INSERT INTO pengguna (password, username, nama, umur, agama, pekerjaan, alamat) "
                        + "VALUES ('"+ password +"', '"+ username +"', '"+ nama +"', '"+ umur +"', '"+ agama +"', '"+ pekerjaan +"', '"+ alamat +"')";             
                 s.executeUpdate(sql);   
}
            } catch(SQLException e) {  
             System.out.println("Error pada method setInsert()"); 
             return;
            }