ORA-04054：数据库链接GMAIL.COM不存在

Question

I need help with my college's project(Java web with hibernate and oracle database), this has to edit the users already added previously which have: Mail pk pass typeuser.iduser FK.

add and remove it works but doesnt edit, the error is : javax.servlet.ServletException: java.sql.SQLSyntaxErrorException: ORA-04054: database link GMAIL.COM does not exist

i already tried with using prepared statement but i think i did it wrong

the mail does not need to be edited. only the type of user and password needs it but at the moment of pressing the edit button it shows me the error gmail.com does not exist

<%
            //CONECTANOD A LA BASE DE DATOS:

            Class.forName("oracle.jdbc.OracleDriver").newInstance();
            Connection con = DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:XE", "C##PORTA", "oracle");
            String id = request.getParameter("correo");
            PreparedStatement  stm = con.prepareStatement(id);
            String Query = "select * from usuario where correo=" + id;
            PreparedStatement ps;
            ResultSet rs = stm.executeQuery(Query);
            while (rs.next()) {
        %>``` 

Answer 1

OldProgrammer has shown you the correct way to do this. If you use a PreparedStatement (correctly) it will deal with quoting correctly, and also protect against SQL injection attacks.

The reason you got the obscure error message was that your SQL statement most likely looks something like this after you concatenated it:

 select * from usuario where correo=someone@gmail.com

Since the email address is not quoted, the SQL parser doesn't recognize that as a string literal. Instead, it is treating it as a "db link" as described in CREATE DATABASE LINK .

After you have created a database link, you can use it in SQL statements to refer to tables and views on the other database by appending @dblink to the table or view name.

And that fails because no such database link with the name "gmail.com" has been created.

Answer 2

You are not calling the correct methods with the correct parameters. Should be something like:

        String id = request.getParameter("correo");
        String query = "select * from usuario where correo= ?";
        PreparedStatement  stm = con.prepareStatement(query);
        stm.setString(1, id );
        ResultSet rs = stm.executeQuery();