How can I set all columns' default value equal to null in PostgreSQL

Question

I would like to set the default value for every column in a number of tables equal to Null. I can view the default constraint under information_schema.columns.column_default. When I try to run update information_schema.columns set column_default = Null where table_name = '[table]' it throws "ERROR: cannot update a view HINT: You need an unconditional ON UPDATE DO INSTEAD rule."

What is the best way to go about this?

Answer 1

You need to run an ALTER TABLE statement for each column. Never ever try to do something like that by manipulating system tables (even if you find the correct one - INFORMATION_SCHEMA only contains view to the real system tables)

But you can generate all needed ALTER TABLE statements based on the data in the information_schema views:

SELECT 'ALTER TABLE '||table_name||' ALTER COLUMN '||column_name||' SET DEFAULT NULL;'
FROM information_schema.columns
WHERE table_name = 'foo';

Save the output as a SQL script and then run that script (don't forget to commit the changes)