Re: Function to return per-column counts?

On Thu, Sep 28, 2017 at 3:31 PM, Seamus Abshere <seamus(at)abshere(dot)net> wrote:

> > > > Does anybody have a function lying around (preferably pl/pgsql) that
> > > > takes a table name and returns coverage counts?
> > >
> > > What is "coverage count"?
>
> Ah, I should have explained better. I meant how much of a column is
> null.
>
> Basically you have to
>
> 0. count how many total records in a table
> 1. discover the column names in a table
> 2. for each column name, count how many nulls and subtract from total
> count
>
> If nobody has one written, I'll write one and blog it.
>
> Thanks!
> Seamus
>
> PS. In a similar vein, we published
> http://blog.faraday.io/how-to-do-histograms-in-postgresql/ which gives
> plpsql so you can do:
>
> SELECT * FROM histogram($table_name_or_subquery, $column_name)
>
> --
> Seamus Abshere, SCEA
> https://www.faraday.io
> https://github.com/seamusabshere
> https://linkedin.com/in/seamusabshere
>
>
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I can't really do the full query for you, but the following should be able
to give you a head start:

SELECT c.relname AS table,
a.attname AS column,
a.attnum AS colnum,
s.stanullfrac as pct_null,
s.stadistinct
FROM pg_class c
JOIN pg_attribute a ON a.attrelid = c.oid
JOIN pg_statistic s ON (s.starelid = c.oid AND s.staattnum = a.attnum)
WHERE c.relname = 'your_table_name'
AND a.attnum > 0
ORDER BY 3

--
*Melvin Davidson*
I reserve the right to fantasize. Whether or not you
wish to share my fantasy is entirely up to you.