At 05:57 AM 11/26/2002 +0000, mikeevteev wrote:

>Table is ... just a table. Nothing special, just a lot of char fields.
>Main point is it has index, lets say on field named field_a.
>
>Query is stupid of cource: select field_a from table
>
>I just guess that reading index is cheaper then reading all data pages
>in that case, becouse index cover all fields in query.
>But optimizer select plan with natural.

Firebird indexes reflect the multi-generational data representation,
so they often contain entries that are not valid for all transactions.
The only way to verify that the data is valid for your transaction
is to read the actual record. That being the case, the fastest way
to read all the records in the table is to start with the first data
page and go forward, in other words, NATURAL.

>Another question related to optimazer.
>Table is same.
>Query select field_a from table
>Optimizer plan SORT(table NATURAL).
>
>Why SORT? Here is index already. All fields is covered!

Beats me. Did your query have an order by clause that you
neglected to include?


Regards,

Ann
www.ibphoenix.com
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