cannot drop table users because other objects depend on it

Question

I want to drop my tables in database. But, when I use, for example, DROP TABLE if exists users; I receive this message:

cannot drop tab

Answer 1

Use the cascade option:

DROP TABLE if exists users cascade;

this will drop any foreign key that is referencing the users table or any view using it.

It will not drop other tables (or delete rows from them).

Answer 2

If it was really necessary to drop that specific table with or without recreating it, then first find the object(s) that depends on it.

CREATE OR REPLACE VIEW admin.v_view_dependency AS 
SELECT DISTINCT srcobj.oid AS src_oid
  , srcnsp.nspname AS src_schemaname
  , srcobj.relname AS src_objectname
  , tgtobj.oid AS dependent_viewoid
  , tgtnsp.nspname AS dependant_schemaname
  , tgtobj.relname AS dependant_objectname
FROM pg_class srcobj
  JOIN pg_depend srcdep ON srcobj.oid = srcdep.refobjid
  JOIN pg_depend tgtdep ON srcdep.objid = tgtdep.objid
  JOIN pg_class tgtobj ON tgtdep.refobjid = tgtobj.oid AND srcobj.oid <> tgtobj.oid
  LEFT JOIN pg_namespace srcnsp ON srcobj.relnamespace = srcnsp.oid
  LEFT JOIN pg_namespace tgtnsp ON tgtobj.relnamespace = tgtnsp.oid
WHERE tgtdep.deptype = 'i'::"char" AND tgtobj.relkind = 'v'::"char";

Then,

select top 99 * from admin.v_view_dependency where src_objectname like '%the_table_name_it_complaint_about%';

The result set will show you the dependant object in the field "dependant_objectname".

Answer 3

In general, to drop several interdependent tables you start from the tables that nothing depends on (the ones that have foreign keys pointing to other tables), and work backwards. E.g., if the table transactions depends on the table users, you'd drop transactions first. In short: Delete tables in the reverse order from how they were created.

If you manage to create tables with circular dependencies, you can first delete the foreign key constraint that prevents deletion. Or you can use the modifier CASCADE, which (as @a_horse explained in the comments), will drop any foreign key constraints that involve the deleted table. But note that not all DBMS's support CASCADE: Postgres does, but MySQL does not (the keyword is accepted but has no effect).