Re: Count of non-null values per table column

On Fri, Aug 14, 2015 at 9:59 AM, John McKown <john(dot)archie(dot)mckown(at)gmail(dot)com>
wrote:
>
> David,
>
> It still came through as junk. But I reconstructed it below
>
> === original message ===
> Apologies if this has been asked before. My search only turned up ways to
list the total non-null values for all columns as a single number. I want
the count for each column by column.
>
> I have inherited a database consisting of two related huge monolithic
tables that lack referential integrity between them, or even basic data
constraints. One of the problems these tables have is every single non-PK
column is NULLable. I am trying to understand the information that is
actually stored and used so that I can implement a (hopefully) better
design. Towards that end I would like to know the count of non-null values
in each column per column. In other words I would like to get the following
output from a table (the numbers are totally made up):
>
> column_name | num_values
> ------------+-----------
> col1 | 5787
> ------------+-----------
> col2 | 17
> ------------+-----------
> col3 | 567
> ------------+-----------
> col4 | 5787
> ------------+-----------
> col5 | 143
> ------------+-----------
> col6 | 1
> ------------+-----------
>
> ====
>
> I assume what "num_values" contains is the _distinctly different_ number
of values in "column_name" for each and every column name in a table. E.g.
if "col1" contains value 'x' twice and 'y' ten times,then "num_values"
would be 2, not 12. Or do you really want the 12? I'm unsure.
>

Thanks John for fixing that which microsoft screwed up, and I've switched
to my gmail account for this.

For my purposes 12 would be fine. I just want to know of the total number of
rows in the table, how many have a value in each column. I guess I'm
actually trying to get the complement of the number of NULLs per column in
the end.

BTW, aplologies for omitting basic info:
SELECT version();
version

----------------------------------------------------------------------------------------------------------------
PostgreSQL 9.1.18 on x86_64-unknown-linux-gnu, compiled by gcc (GCC) 4.4.7
20120313 (Red Hat 4.4.7-11), 64-bit

>
>
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>
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>
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>
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> Maranatha! <><
> John McKown