Oracle 10g - optimize WHERE IS NOT NULL

Question

We have Oracle 10g and we need to query 1 table (no joins) and filter out rows where 1 of the columns is null. When we do this - WHERE OurColumn IS NOT NULL - we get a full

Answer 1

It can depend on the type of index you have on the table.

Most B-tree indexes do not store null entries. Bitmap indexes do store null entries.

So, if you have:

select * from mytable where mycolumn is null

and you have a standard B-tree index on mycolumn, then the query can't use the index as the "null" isn't in the index.

(If the index is against multiple columns, and one of the indexed columns is not null then there will be an entry in the index.)