title: Why does postgres group null values?
body: <pre><code>CREATE TEMP TABLE wirednull (
      id bigint NOT NULL,
      value bigint,
      CONSTRAINT wirednull_pkey PRIMARY KEY (id)
  );
  INSERT INTO wirednull (id,value) VALUES (1,null);
  INSERT INTO wirednull (id,value) VALUES (2,null);
  
  SELECT value FROM wirednull GROUP BY value;
  </code></pre>
  
  <p>Returns one row, but i would expect two rows since</p>
  
  <pre><code>SELECT * 
  FROM wirednull a 
  LEFT JOIN wirednull b 
    ON (a.value = b.value)
  </code></pre>
  
  <p>does not find any joins, because null!=null in postgres</p>