Every database-developer know the sql-statement "where column IS NULL", no problem I think
BUT how can you extend the statement into "where column1 IS NULL = column2 I IS NULL" ??
This type of query is IMO not defined in the SQL-standard or possible with a SQL-database, or ?
In Oracle 10g is an undocumented function: sys_op_map_nonnull
...where sys_op_map_nonnull(column1)=sys_op_map_nonnull(column2) ...
this makes sometimes my developer-life easier