When / how are default value expression functions bound with regard to search_path?

Question

For testing purposes, I provide my own implementation of the now() function which is public.now(). Using search_path to override the defau

Answer 1

The default function is "bound" at the time the default constraint is created. The view showing the unqualified name is simply abbreviating it.

This can be demonstrated by inserting rows before and after shadowing the function:

Set search_path to public,pg_catalog;

Create Temp Table foo (
    test date not null default now()
);

Insert Into foo default values;

Create Function public.now() Returns timestamp with time zone Language SQL As $$ 
     -- No idea why I chose this date.
     Select '1942-05-09'::timestamp with time zone;
$$;

Insert Into foo default values;

Select * from foo;

Note that both rows (inserted before and after function creation) contain today's date, not the fake date.

Furthermore, creating a table with the above function already in scope, then trying to delete the function, results in a dependency error:

Set search_path to public,pg_catalog;

Create Function public.now() Returns timestamp with time zone Language SQL As $$ 
    Select '1942-05-09'::timestamp with time zone;
$$;

Create Temp Table bar (
    test date not null default now()
);

Insert Into bar default values;

Select * from bar;
-- Single row containing the dummy date rather than today

Drop Function public.now();
-- ERROR:  cannot drop function now() because other objects depend on it

If the binding happened only on insert, there would be no such dependency.