null handling: WHERE clause "IS NULL" versus "=?" and setNull

[Mark Addleman]

Attached is a test case that demonstrates a difference in how where clause handles NULL.  In the first case, my SELECT includes "WHERE c IS NULL"  My second case has "WHERE c=?" and then I do preparedStatement.setNull(1, Types.VARCHAR).  The queries return different results.  There must be some difference in the semantics of the two queries but I don't know what it is.  Can someone explain it?  Thanks