Cannot drop table <table> because other objects depend on it

Suppose you have 2 tables, namely foo and foo_old, each having a column called "id".

Suppose both tables have the following schema:

id integer NOT NULL DEFAULT nextval('foo_id_seq'::regclass)

and you want to DROP the foo_old table:

test=# DROP TABLE foo_old;
ERROR: cannot drop table foo_old because other objects depend on it
DETAIL: default for table foo column id depends on sequence foo_id_seq
HINT: Use DROP ... CASCADE to drop the dependent objects too.

You do not want to drop the sequence as the other table, foo, relies on it. Therefore, CASCADE is not an option.

The problem here is that the sequence has a dependency with the other table / column.

You can check who owns the sequence with the \d+ meta-command from psql:

test=*# \d+ foo_id_seq
Sequence "public.foo_id_seq"
Type | Start | Minimum | Maximum | Increment | Cycles? | Cache 
bigint | 1 | 1 | 9223372036854775807 | 1 | no | 1
Owned by: public.foo_old.id

test=*# 

You can alter the sequence so it is owned by the other table:

test=*# ALTER SEQUENCE public.foo_id_seq OWNED BY public.foo.id;
ALTER SEQUENCE

Then, re-check the sequence:

test=*# \d+ foo_id_seq
Sequence "public.foo_id_seq"
Type | Start | Minimum | Maximum | Increment | Cycles? | Cache 
bigint | 1 | 1 | 9223372036854775807 | 1 | no | 1
Owned by: public.foo.id

Now you can DROP the foo_old table:

test=*# DROP TABLE foo_old;
DROP TABLE
test=*#

The sequence has a dependency with a column of the table that you want to drop.