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Asked: 2026-05-20T08:04:09+00:00

As always, I apologize if this is a stupid question (two questions, actually). I’m

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As always, I apologize if this is a stupid question (two questions, actually). I’m not a DBA, so I know very little about indexes. My questions are:

  1. Is there any cutoff point (in terms of number of rows) at which an index would be pointless? For example, is there any benefit to an index on a lookup table with 10-20 rows?

  2. I’ve read some things about covering indexes in Oracle, and the concept makes sense in that the data can be retrieved directly from the index and a trip to the table is unnecessary. How can I tell if an index is a covering index? Is this a value set when the index is created, or by default based on the rows that the index includes?

I hope this makes sense.

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  1. Editorial Team

    Richard Foote has a series of blog posts on indexes for small tables. The short answer is probably not (but the long answer is much more interesting).

    A covering index is a general term for an index that contains all the columns that are part of either the SELECT list or the WHERE clause for a table. It is not a property of an index– any index can be a covering index for some query. It is something that is specific to a query and to the indexes available to the optimizer.

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