Comment by dotancohen

  > mysql> select 42=42,42=314,42=null,null=null;
  > +-------+--------+---------+-----------+
  > | 42=42 | 42=314 | 42=null | null=null |
  > +-------+--------+---------+-----------+
  > |     1 |      0 |    NULL |      NULL |
  > +-------+--------+---------+-----------+

I see, thank you. This behaviour is news to me.