Checking if user exists in Oracle Database - java jdbc

Question

So I have this working code/prepared statement that adds a username and password into a database, however I need to check if the username already exists in the code.

public void addUser(Connection conn, PreparedStatement pstmnt, String username, String password) 
    {
        try 
        {
            pstmnt = conn.prepareStatement("insert into users values (?,?,?)");
            pstmnt.setInt(1, 0);
            pstmnt.setString(2, username);
            pstmnt.setString(3, password);
            pstmnt.executeUpdate();
        } 
        catch (SQLException e) { System.out.println("Error: " + e.getMessage()); }

        System.out.println(username + " has been added");
    }

Is there any simple way to do this?

Answer 1

您可以在数据库中添加唯一约束，并相应地在addUSer中处理异常

Answer 2

If there's no many duplicate key risk, you can just try and check the error code if it matches "dup key error" ( Error ORA-00001 ).

Else you must lock the entire table, check for key existence, update and then commit (which release the lock)