Is that we can add a column to the existing index

Hello

I did some research but I just want to get some clarification

I have an index create index n1 on emp (comm);

now I want to add a sal column in this index n1, an option is droping and create the index, can we just add a column with falls, more (regarding my review and research, we can not do, but just confirm with you)

If we are unable to add it, I want to know the reason behind it, why we can not do?


Thank you
Sunil Noothi

The reason why you can't just add a column to an index has to do with the nature of a Btree index. A Btree index is structured in a very special way, so that all the index entries appear in the order when the index is read. Essentially, all indexes are unique indexes. Those who are not declared unique add ID to the key in order to get a unique sort order.

If you just add another column to the index, there is no guarantee (and in fact, it would be extremely unlikey) that the new column would sort in exactly in the same way as the old column more the rowid. So, to add a column to the index, the entire structure should be demolished to maintain good order sorted, which would be at least the same amount of work as a creation of the index of zero and probably more work.

John

Tags: Database

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