ERROR: no schema has been selected to create in

This happens when not having USAGE privilege on any of the schemas of search_path. By default the pseudo-role public (all users) has this privilege on the publicschema, so this error happens only after revoking it explicitly with:

revoke usage on schema public from public;

This is required when it's not desirable that people peek into other people schemas, even without selecting data from tables (which is granted through different privileges).

If this REVOKE hasn't been done in that database, it may have happened in the template database by which new databases are modelled (see CREATE DATABASE).

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When a user has USAGE privilege, but lacks CREATE privilege on the schema, it's a different error when trying to create an object: permission denied for schema public.

To check the privileges inside psql, use \dn+ public.

By default (shown with extended display \x for readability):

# \dn+ public
List of schemas
-[ RECORD 1 ]-----+-----------------------
Name              | public
Owner             | postgres
Access privileges | postgres=UC/postgres
                  | =UC/postgres
Description       | standard public schema

lack of a rolename before = means it's for all roles (=public)

Without public USAGE privilege

Name              | public
Owner             | postgres
Access privileges | postgres=UC/postgres
                  | =C/postgres
Description       | standard public schema

Without public USAGE or CREATE privileges

Name              | public
Owner             | postgres
Access privileges | postgres=UC/postgres
Description       | standard public schema

I had pgdump file with creating functions in custom schema and I wanted to switch custom schema name to general public and replaced all occurences with old schema to empty (e.g. myschema.tablename to tablename) And started to receive error

ERROR:  no schema has been selected to create in

For my case error happens when at the beginning of dump present line

SELECT pg_catalog.set_config('search_path', '', false);

I have changed second arg to "public"

SELECT pg_catalog.set_config('search_path', 'public', false);

And problem gone

I've tried multiple solutions, and keep getting the same error over and over.

Worse to mention, the error appears to me when I needed to restart migration of my DB by deleting public schema and after creating it again.

The fix was:

grant usage on schema public to public;
grant create on schema public to public;