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To: pgsql-sql@postgresql.org
From: Rainer Stengele <rainer.stengele@diplan.de>
Subject: grouping subsets
Date: Thu, 22 Jul 2010 10:09:16 +0200
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Hi,

having a table similar to

| 1 | B | [2010-07-15 Do] |
| 1 | B | [2010-07-16 Fr] |
|---+---+-----------------|
| 2 | C | [2010-07-17 Sa] |
| 2 | C | [2010-07-18 So] |
|---+---+-----------------|
| 1 | B | [2010-07-19 Mo] |
| 1 | B | [2010-07-20 Di] |
| 1 | B | [2010-07-21 Mi] |
| 1 | B | [2010-07-22 Do] |
|---+---+-----------------|
| 3 | D | [2010-07-23 Fr] |

a simple group by gives me:

| 6 | B |
| 4 | C |
| 3 | D |


What I want to get is the values grouped by "subset", where a subset is a set of rows with identical column until the colum changes.
Is there a way to get

| 2 | B |
| 4 | C |
| 4 | B |
| 3 | D |

by SQL only?

- Rainer