| From: | Sergey Konoplev <gray(dot)ru(at)gmail(dot)com> |
|---|---|
| To: | Andrew Taylor <andydtaylor(at)gmail(dot)com> |
| Cc: | pgsql-general <pgsql-general(at)postgresql(dot)org> |
| Subject: | Re: Join query query |
| Date: | 2013-02-13 23:24:18 |
| Message-ID: | CAL_0b1tRjF4ZkeN3cS_2V00tXbPoQK9x1Q+rWA6dFnMz9+1e+g@mail.gmail.com |
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| Lists: | pgsql-general |
On Wed, Feb 13, 2013 at 3:01 PM, Andrew Taylor <andydtaylor(at)gmail(dot)com> wrote:
> And ended up with a table 13,708,233 rows long with what looks like plenty
> of duplicated rows. Some but not all are duplicated. What can I do to sort
> this out?
It means that (e, n) pairs are not unique in A and B and you got a
superposition of them. If you have 5 equal pairs in A and 7 same pairs
with in B you will get 35 combinations as a result.
And BTW when you use LEFT JOIN if there are rows in A that have no
matching pairs in B you will get one row for each of them where lan
and lon are NULLs.
See the join_type section here
http://www.postgresql.org/docs/9.2/static/sql-select.html.
--
Sergey Konoplev
Database and Software Architect
http://www.linkedin.com/in/grayhemp
Phones:
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