Postgresql – “ERROR: column rel.relhasoids does not exist” with PostgreSQL 12 and PgAdmin 4.3

Other than not using features that cause errors, no, there is no workaround. Since in this case one of the features that causes an error appears to be listing tablespaces during startup, you're out of luck.

Just compile a newer version of PgAdmin-III from sources or use the command-line psql client that comes with PostgreSQL 9.2.

PostgreSQL's system catalogs aren't 100% compatible from version to version. That's intentional; if they had to be exactly the same it'd be very hard to make changes and improvements to PostgreSQL. Programs that use the system catalogs should be prepared to require updates when a new PostgreSQL version comes out. Most tools that use the catalogs - like psql, PgAdmin-III, pg_dump, etc - do so because it's the only way to get detailed information about some of the inner workings of the system. You just need to update them when you update the server.

Your issue is that you have defined a recursive function ... the function is calling itself. The logic that exists in it currently would result in a stack dump with OUT OF MEMORY error (or something along those lines, at least) if it didn't give you the error of "table already exists" to begin with..

CREATE OR REPLACE FUNCTION f_copy_tbl(_tbl regclass, _newtbl text)
 RETURNS void AS
$func$
BEGIN

--<snip stuff>

--Now populate `parts1` table with `parts` table's content...
SELECT f_copy_tbl('parts','parts1');  --- THIS IS THE OFFENDING LINE HERE .. REMOVE IT
INSERT INTO parts1 SELECT * FROM parts;

--<snip stuff>

END
$func$ LANGUAGE plpgsql VOLATILE;

Your order of SQL should be as such:

CREATE OR REPLACE FUNCTION my_func(param1 VARCHAR, param2 VARCHAR) RETURNS VOID AS $$
DECLARE
  var1 VARCHAR;
BEGIN
  -- DO STUFFS HERE FOR FUNCTION
END;
$$ LANGUAGE plpgsql;
-- THE ABOVE DEFINES THE FUNCTION

-- THE BELOW EXECUTES THE FUNCTION
SELECT my_func('val1', 'val2'); -- THIS ONE LINE WILL EXECUTE ALL SQL DEFINED INSIDE THE FUNCTION

The function definition is what is between the dollar quoting..