Thanks !
However, I tried what you suggested and there was no change.
I used EXPLAIN QUERY PLAN on the query and it looks like it does not use
any index on b at all, only if I use hardcoded conditions like b > 0.
It appears that the real problem is that SQlite does not use indices for
both tables, e.g.:
CREATE INDEX a_chr on a(chr)
CREATE INDEX b_chr on b(chr)
explain query plan
select a.chr, b.chr
from b, a
where b.chr = a.chr;
Output:
0 0 TABLE b
1 1 TABLE a WITH INDEX a_chr
There is an example on how to use multiple indices on the same table
here: http://www.sqlite.org/cvstrac/wiki?p=PerformanceTuning
However, I'm not sure how to extend this to joined tables.
Thanks !
Best regards,
Hilmar
El 10/14/2010 7:12 PM, Simon Slavin escribió:
> On 14 Oct 2010, at 5:46pm, Hilmar Berger wrote:
>
>> The query is as follows:
>>
>> select * from
>> a, b
>> where a.chr = b.chr and a.strand = b.strand and a.start<= b.start
>> and a.stop>= b.stop and b.start<= a.stop and a.start<= b.stop ;
>> Indexes has been created for all fields in A and B (e.g.
>> create index name on A(chr, start, stop, strand));
> I not certain from your phrasing, but this may not do what you think. It is
> different matter to do
>
> create index Achr on A (chr)
> create index Astart on A (start)
> create index Astop on A (stop)
> ...
>
> to what you did above. One creates one index on the sequence of four
> variables, the other creates four indexes each on one variable.
>
> However, to make this SELECT go fast,
> CREAT INDEX Bkey ON B (chr,strand)
> CREAT INDEX Bstart ON B (start)
> CREAT INDEX Bstop ON B (stop)
>
> May help.
>
> Also I recommend doing this:
>
> http://www.sqlite.org/lang_analyze.html
>
> Simon.
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