Issue with NULL varchars

Hi,

I'm relatively knew to PostgreSQL, but have a fair amount of
experience with JDBC and Oracle/SQL Server.

I'm running PostgreSQL 8.3.0 on Mac OSX 10.5.2, am using the 8.3-603
JDBC drivers, and using Java 1.5.0_13.

I'm a bit confused by the results of the following test case code:

----

import java.sql.*;

public class jdbcLocaleTest
{
public static void main(String args[])
{
try
{
Driver driver = (Driver)
Class.forName("org.postgresql.Driver").newInstance();
DriverManager.registerDriver(driver);
Connection c =
DriverManager.getConnection("jdbc:postgresql://localhost/testdb",
"testdb", "");

int count, id = 1;
PreparedStatement p;
ResultSet rs;

String language = "en";
String country = "GB";
String variant = null;

// Create a test table:
p = c.prepareStatement("CREATE TABLE testing (id int, language
varchar(2), country varchar(2), variant varchar(64))");
p.execute();

// Create a new Locale in the database:
p = c.prepareStatement("INSERT INTO testing (id, language,
country, variant) VALUES (?, ?, ?, ?)");
p.setInt(1, id);
p.setString(2, language);
p.setString(3, country);
p.setNull(4, java.sql.Types.VARCHAR); // or p.setString(4, variant);
count = p.executeUpdate();
System.out.println("INSERT: inserted " + count + " rows.");

// Retrieve that Locale by its ID:
p = c.prepareStatement("SELECT language, country, variant FROM
testing WHERE id = ?");
p.setInt(1, id);
rs = p.executeQuery();
while (rs.next())
{
System.out.println("SELECT by id: language=" + rs.getString(1)
+ ", country=" + rs.getString(2) + ", variant=" + rs.getString(3));
}
rs.close();

// Retrieve that Locale's ID by its Data:
p = c.prepareStatement("SELECT id FROM testing WHERE language =
? AND country = ? AND variant = ?");
p.setString(1, language);
p.setString(2, country);
p.setNull(3, java.sql.Types.VARCHAR); // or p.setString(3, variant);
rs = p.executeQuery();
while (rs.next())
{
System.out.println("SELECT by data: Got id=" + rs.getInt(1));
}
rs.close();

// Retrieve that Locale's ID by its Data:
p = c.prepareStatement("SELECT COUNT(*) FROM testing WHERE variant = ?");
p.setNull(1, java.sql.Types.VARCHAR); // or p.setString(1, variant);
rs = p.executeQuery();
while (rs.next())
{
System.out.println("SELECT COUNT: count=" + rs.getInt(1));
}
rs.close();

// Drop the test table:
p = c.prepareStatement("DROP TABLE testing");
p.execute();

p.close();
}
catch (Exception e)
{
System.out.println("Error: " + e);
}
}
}

----

The output, when I run this, is

INSERT: inserted 1 rows.
SELECT by id: language=en, country=GB, variant=null
SELECT COUNT: count=0

which implies that the table is created, the row is inserted, the row
is retrieved when selecting by its Id, but when we try and search for
anything with a NULL varchar value, nothing is returned.

I've also tried swapping the setNull statements with setString(n,
null) - same result.

What am I missing?!

Many thanks,

Ant.