| Subject | Re: Slow query (unindexed reads) |
|---|---|
| Author | kerryneighbour |
| Post date | 2011-06-22T12:41Z |
--- In firebird-support@yahoogroups.com, Svein Erling Tysvær <svein.erling.tysvaer@...> wrote:
When I do a join on another table - THAT table also reads in in non indexed as well (even though there are indexes on the join fields). Same problem, I am thinking.
I do not care about the ORDER BY - I don't care about the order the records are processed in. I simply use it to try and force the use of an index. It did not work in this case, but I seem to recall it working in other cases.
>In this case I need to traverse the whole table - and I join to a couple of others for lookup values. It is not for display, and there are a few WHERE clauses in the final query. The real query takes over 7 minutes..which is totally unacceptable. I pared it right down to see if the non indexed read is the problem. As far as I can see, the indexes are not being used.
> Stop thinking tables, start thinking datasets!
>
> Indexes are useful in WHERE and JOIN clauses, selects that return entire tables normally don't benefit much from using an index (it might be a bit quicker or slower, but the difference isn't huge).
>
When I do a join on another table - THAT table also reads in in non indexed as well (even though there are indexes on the join fields). Same problem, I am thinking.
I do not care about the ORDER BY - I don't care about the order the records are processed in. I simply use it to try and force the use of an index. It did not work in this case, but I seem to recall it working in other cases.