How to drop all NOT NULL constraints from a PostgreSQL table in one go

Question

Is it possible to drop all NOT NULL constraints from a table in one go?

I have a big table with a lot of NOT NULL constraints and I'm searching for a solution that is faster than dropping them separately.

Answer 1

You can group them all in the same alter statement:

alter table tbl alter col1 drop not null,
                alter col2 drop not null,
                …

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You can also retrieve the list of relevant columns from the catalog, if you feel like writing a do block to generate the needed sql. For instance, something like:

select a.attname
  from pg_catalog.pg_attribute a
 where attrelid = 'tbl'::regclass
   and a.attnum > 0
   and not a.attisdropped
   and a.attnotnull;

(Note that this will include the primary key-related fields too, so you'll want to filter those out.)

If you do this, don't forget to use quote_ident() in the event you ever need to deal with potentially weird characters in column names.