

NULL in the Oracle Database — Is it special, or strange, or just wrong? - fatalmind
http://use-the-index-luke.com/sql/where-clause/null

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chris_wot
Wrong. NULL means that data is missing. A blank string is not missing data, it
is actually data that says that the string is empty. By making an empty string
NULL, it causes havoc with query joins, because an inner join against a NULL
value will never return the rows. But you may _want_ to join empty string
values.

Also, if you add NULL to an IN(...) clause, it will return nothing at all. If
you do a subselect that returns an empty string, then this will stop the query
from working.

More traps for young players. Can't believe Oracle hasn't fixed this yet!

