Postgres 16

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create function f(arg1 int) returns int as $f$ select arg1 $f$ language sql;

CREATE FUNCTION

select f(42), f('77');--one works as intended, one thanks to type coercion

f
f

42
77

SELECT 1

select f('1'::text);--explicit type cast disables coercion

ERROR:  function f(text) does not exist
LINE 1: select f('1'::text);--explicit type cast disables coercion
               ^
HINT:  No function matches the given name and argument types. You might need to add explicit type casts.

create function f(variadic args anycompatiblearray) returns int as $f$ 
begin raise exception 'MY CUSTOM MESSAGE: UNRECOGNIZED f() PARAMETER TYPES';
end $f$ language plpgsql;

CREATE FUNCTION

select f('a'::text);

ERROR:  MY CUSTOM MESSAGE: UNRECOGNIZED f() PARAMETER TYPES
CONTEXT:  PL/pgSQL function f(anycompatiblearray) line 2 at RAISE

create table test as select 'a'::text as column1;
select f(column1) from test;

SELECT 1

ERROR:  MY CUSTOM MESSAGE: UNRECOGNIZED f() PARAMETER TYPES
CONTEXT:  PL/pgSQL function f(anycompatiblearray) line 2 at RAISE

--doesn't work with unknown literals
select f('a');

ERROR:  function f(unknown) is not unique
LINE 2: select f('a');
               ^
HINT:  Could not choose a best candidate function. You might need to add explicit type casts.

create function f(args unknown) returns int as $f$ 
begin raise exception 'MY CUSTOM MESSAGE: UNRECOGNIZED f() PARAMETER TYPES';
end $f$ language plpgsql;

ERROR:  PL/pgSQL functions cannot accept type unknown

create function f(args unknown) returns int as $f$ select f(args::text) $f$ language sql;

ERROR:  SQL functions cannot have arguments of type unknown

alter function f(int) rename to f_another_name;
create or replace function f(variadic args anycompatiblearray) returns int as $f$ 
begin return f_another_name(args[1]::int);--this pass-through can get complicated
exception when others then 
  raise exception 'MY CUSTOM MESSAGE: UNRECOGNIZED f() PARAMETER TYPES';
end $f$ language plpgsql;

ALTER FUNCTION

CREATE FUNCTION

--now even unknowns go there because there's just one f(), accepting all calls
select f('a');

ERROR:  MY CUSTOM MESSAGE: UNRECOGNIZED f() PARAMETER TYPES
CONTEXT:  PL/pgSQL function f(anycompatiblearray) line 4 at RAISE

select f(88),f('99');--regular calls still work thanks to the pass-through

f
f

88
99

SELECT 1