Why doesn't preparedStatement work when working with Postgres?

Question

PostgreSQL

package com.company.Labs.Lab_6;

import java.sql.*;


public class Final_test {
    public void ex1() {

        try {
            //Задание 1
            Connection connection = DriverManager.getConnection("jdbc:postgresql://localhost:5432/testDB", "postgres", "1703");
            Statement statement = connection.createStatement();


            statement.execute("drop table if exists students");
            statement.execute("create table students (ID int primary key not null, NAME varchar(20) not null" +
                    ", AGE int not null , STUDY_OR_NOT boolean not null, HEIGHT float not null)");

            PreparedStatement preparedStatement = connection.prepareStatement("insert into students (ID,NAME,AGE,STUDY_OR_NOT,HEIGHT) values (?,?,?,?,?)");

            preparedStatement.setInt(1, 1);
            preparedStatement.setString(2, "Daniil");
            preparedStatement.setInt(3, 20);
            preparedStatement.setBoolean(4, true);
            preparedStatement.setFloat(5, 1.82f);

            int n = preparedStatement.executeUpdate();
            System.out.println(n); // выводит 1, то есть все крашится на том, что id, якобы повторяется и я его будто 2 раза записываю.


            ResultSet resultSet = statement.executeQuery("select * from students");
            while (resultSet.next()) {

                int id = resultSet.getInt(1);
                String name = resultSet.getString(2);
                int age = resultSet.getInt(3);
                boolean study_or_not = resultSet.getBoolean(4);
                float height = resultSet.getFloat(5);
                preparedStatement.executeUpdate();

                System.out.println(id + "/" + name + "/" + age + "/" + study_or_not + "/" + height);
            }

            statement.close();
            preparedStatement.close();
            connection.close();
        } catch (SQLException e) {
            System.err.println(e);
        }

    }
}

org.postgresql.util.PSQLException: ERROR: Duplicate key value violates unique constraint 'students_pkey'
Details: Key '(id)=(1)' already exists.

for me it's so strange, because I only set the value once for each field, and then I read them once. Generally a strange topic.

Answer 1

Because you already have a record in the database with primary key 1. The problem is not in PostgreSQL and not in preparedStatement.

Answer 2

I’ll just add to the answer of Sergey Gornostaev
Try to set a different id in this line You
preparedStatement.setInt(1, 1);
have a violation of the uniqueness of the primary key and, accordingly, you need to specify a different identifier other than 1