Postgres 9.6

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create function f(int)
returns int
language sql
as 'select $1';

CREATE FUNCTION


do $$
begin
  create function f (int)
  returns int
  language sql
  as 'select $1';
end; $$

ERROR:  function "f" already exists with same argument types
CONTEXT:  SQL statement "create function f (int)
  returns int
  language sql
  as 'select $1'"
PL/pgSQL function inline_code_block line 3 at SQL statement


do $$
begin
    create function f (int)
    returns int
    language sql
    as 'select $1';
    

  exception
    when duplicate_function then
    null;
end; $$
    

DO