From: Ashish Ahlawat <ahlawat.ashish@gmail.com>
To: Ragnar <gnari@hive.is>
Cc: Dirk Griffioen <dirk@code-shop.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: join and sort on 'best match'
Date: Thu, 14 Dec 2006 18:40:53 +0530
Message-ID: <682126990612140510j61d2268fq80235b02a550eccd@mail.gmail.com> (raw)
In-Reply-To: <1166005787.6369.79.camel@localhost.localdomain>
References: <457FC751.6080104@code-shop.com>
<1166005787.6369.79.camel@localhost.localdomain>
hi pls tell me ----
if table *Item 3 : news, nature, greenpeace, whale has all clmn y v need
join ??*
*Ashish*
On 12/13/06, Ragnar <gnari@hive.is> wrote:
>
> On mið, 2006-12-13 at 10:26 +0100, Dirk Griffioen wrote:
>
> > I have been breaking my head on the following problem: how to join 2
> > tables and sort the results on the best match.
> ^^^^^^^^^^^^^
> > - there are 3 tables, items, tags and items_tags. The items_tags table
> > links items to tags.
> > - I have one item which has certain tags, and I want to look up all
> > the other items that have those tags as well
>
> looks to me like you want to join:
> items->item_tags->tags->item_tags->items
>
> so the basic select is:
> SELECT *
> FROM items AS i1
> JOIN items_tags AS it1 ON (it1.item_id = i1.id)
> JOIN tags AS t ON (t.tag_id = it1.tag_id)
> JOIN items_tags AS it2 ON (it2.tag_id = t.tag_id)
> JOIN items AS i2 ON (i2.id = it2.item_id)
> WHERE i1.id=?
>
> > - results should be sorted and presented by 'best match': first all
> > the items that have 3 tags in common, then 2 and last 1
>
> this would be:
>
> SELECT i1.id,i2.id,COUNT(*) as quantity
> FROM items AS i1
> JOIN items_tags AS it1 ON (it1.item_id = i1.id)
> JOIN tags AS t ON (t.tag_id = it1.tag_id)
> JOIN items_tags AS it2 ON (it2.tag_id = t.tag_id)
> JOIN items AS i2 ON (i2.id = it2.item_id)
> WHERE i1.id=?
> GROUP by i1.id,i2.id
> ORDER BY quantity DESC
>
> > I thought I had found the solution (my test cases worked), but I now
> > find cases that should be found by the query but are not.
>
> if this does not work, please provide us with a counter example.
>
> gnari
>
>
>
> ---------------------------(end of broadcast)---------------------------
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>
> http://archives.postgresql.org
>
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To: pgsql-sql@postgresql.org
Cc: ahlawat.ashish@gmail.com, gnari@hive.is, dirk@code-shop.com
Subject: Re: join and sort on 'best match'
In-Reply-To: <682126990612140510j61d2268fq80235b02a550eccd@mail.gmail.com>
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