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Set returning aggregate? - Mailing list pgsql-general

From Bborie Park
Subject Set returning aggregate?
Date
Msg-id CAKVfRvHJhL0ZQN+FaJTgZqNTcV+6ae-wCKz=iUpugJdtQZ7rJw@mail.gmail.com
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Responses Re: Set returning aggregate?  (Pavel Stehule <pavel.stehule@gmail.com>)
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I'm wondering if an aggregate function can return a set of records? 

Say I have a table with a column of type raster (PostGIS). I want to get the number of times the pixel values 1, 3 and 4 occur in that raster column. I am hoping to build an aggregrate function that returns the following...

value | count
--------+--------
1       | 12
--------+--------
2       | 12
--------+--------
3       | 12

Is it possible for an aggregate function to return a set? I've written some test cases and it looks like the answer is No but I'd like confirmation.

Thanks,
Bborie Park

PostGIS Steering Committee

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