create index my_idx on my_table (nvl(column,'null'));
And you can force to use the index you want or the optimizer will choose for you and you can use it in the where clause of a sql query.
Yeah, you can't compare null with something as you can't compare nothing with something, I can't really say, but in most cases nothing == something may return true and the statement will succeed?
Usually in an array or a table when you sort it, search algorithms make null values being at top or bottom, it depends, but the column can be sorted even if it has a null value, you always get null values if you left join a table with other table and don't have all the rows, it makes it null and you can sort by it.
It seems I can't edit my message, but maybe someone could merge it, but when comparing null with something you will get false in most cases, I said it could be true, but just tested it returns false and nothing never seems to be able to be compared and returns false?