why ?????????

[AK]

If I execute a query like , select count(*) from  some_table where 1=2 . why does oracle bothers to look at tables . Since there is only one condition which is false .   If  I write a sql like          select count(*)       from  some_table       where column_a= :a      and a is not null;   it should not even go to look at table , but explain plan suggests that it does a index /table scan  .   -ak