How to differentiate between 0 and null in an INT column in MySQL

Question

If there is a null value stored in a MySQL INT column, it will return 0 when accessed by technoligies like JPA. If 0 value also stored in the column, how can I differentiate between null and 0?

Answer 1

I can't believe, that it is so.
Change primitive type for object type in your entity(Example: int -> Integer)

Answer 2

To differentiate between 0 and NULL you should use ResultSet.wasNull() method, like here:

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;

public class Main {
public static void main(String[] args) throws Exception {    
Connection conn = getConnection();
Statement st = conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,
    ResultSet.CONCUR_UPDATABLE);

st.executeUpdate("create table survey (id int,name varchar(30));");
st.executeUpdate("insert into survey (id,name ) values (1,'nameValue')");
st.executeUpdate("insert into survey (id,name ) values (2,null)");
st.executeUpdate("insert into survey (id,name ) values (3,'Tom')");
st = conn.createStatement();
ResultSet rs = st.executeQuery("SELECT * FROM survey");

while (rs.next()) {
  String name = rs.getString(2);
  if (rs.wasNull()) {
    System.out.println("was NULL");
  } else {
    System.out.println("not NULL");
  }
}

rs.close();
st.close();
conn.close();
}