Dear Richard,
you are right. So Postgres takes a lot of time to get out an
impossible result!
The query I wrote is just a test, the concatenation is only a dummy.
On 19/set/08, at 12:33, Richard Huxton wrote:
> Andrea Moretto wrote:
>> I've got a table called DETAILS, the primary key is : DE_ID char(12),
>> there is another field CO_ID char (12).
>
>> If I run "explain analyze select * from details where co_id ||
>> co_id =
>> '0100760153722324445';" it runs a sequential scan not using the index
>> (which takes about 1000000 times than using the index):
>
> That query can never return any rows. You're appending co_id to itself
> then testing against a non-repeating string. Furthermore it's 19 chars
> long rather than 24. Is this really what you're trying to do?
>
> Read up on "indexes on expressions" in chapter 11 of the manuals, for
> indexing this sort of thing. I don't think it will help you here
> though.
>
> --
> Richard Huxton
> Archonet Ltd
Andrea Moretto
moretto.andrea@gmail.com
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