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From Sam Hough <>
Subject Re: Self Join Query
Date Tue, 14 Apr 2009 16:13:03 GMT

Bit late joining in but since this is the first Google hit for
" joins lucene" thought it was reasonable place to add
this note:

In my application "joins" also start to seem appealing. Almost all my use
cases fit very nicely within what Lucene does apart from a "nice to have" ad
hoc query tool. Here it becomes difficult to "join" the result of queries.

I think the source of this difficulty is that while you can very efficiently
get the two lists of document numbers for matching As and Bs (to use the
original posters example) there is no, obvious, quick way to join the two.
Since document numbers change it would be painful to maintain an external

I started my application years ago before any real full text searching in
postgres etc. Now I'm a bit addicted to how light and fast Lucene on its own

Erick Erickson wrote:
> It's often a mistake to try to force Lucene to act like a database. Is it
> possible to just use the database for the join portion and Lucene
> for the text search?
> Otherwise I agree with Developer Developer. You need to provide
> a higher level idea of *what* it is you're trying to accomplish to get
> good suggestions.
> Best
> Erick
> On Jan 8, 2008 7:23 AM, sachin <> wrote:
>> I need to write lucene query something similar to SQL self joins.
>> My current implementation is very primitive. I fire first query, get the
>> results, based on the result of first query I fire second query and then
>> merge the results from both the queries. The whole processing is very
>> expensive. Doing this is very easy with SQL query as we need to just
>> write self join query and database do the rest for you.
>> What is the best way of implementing the above functionality in lucene?
>> Regards
>> Sachin
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