Count how many percent of values on each column are nulls

Question

Is there a way, through the information_schema or otherwise, to calculate how many percent of each column of a table (or a set of tables, better yet) are NULLs?

Answer 1

In PostgreSQL, you can easily compute it using the statistics tables if your autovacuum setting is on (check it by SHOW ALL;). You can also set the vacuum interval to configure how fast your statistics tables should be updated. You can then compute the NULL percentage (aka, null fraction) simply using the query below:

select attname, null_frac from pg_stats where tablename = 'table_name'