ERROR: requested character too large for encoding

I'm using PostgreSQL 9.6 on Linux.
I got an error when I do a test on chr() function.

postgres=# select chr(1199111);
ERROR:  requested character too large for encoding: 1199111
postgres=# select chr(55296);
ERROR:  requested character not valid for encoding: 55296
postgres=# select chr(100000);
 chr
-----
 
(1 row)

Here, as you can see with value 100k it worked (didn't raise error), however others didn't. I'm curious about that. Could someone please explain to me why ?

I attach test script

do
$
declare 
str text ;
begin
for i in 1..1200000
loop
begin
select chr(i) into str;
exception when others then raise notice '=> i: %     => str: %', i , str ;
#exit; -- you can uncomment this star key
end ;
end loop;
end 
$ ;

UPDATED

postgres=# show server_encoding;
 server_encoding
-----------------
 UTF8
(1 row)

Because it didn't raise an error, doesn't mean it worked. None of these work, but only one of them is so absurd as to make chr() explode.

• 100000 (186A0) maps to the Supplementary Multilingual Plane, but there is nothing there (yet).

• 55296 (U+D800) maps to the Basic Multilingual Plane, but nothing is there (yet).

• 1199111 (U+124C07) is not even valid, it maps to a plane so high that Unicode doesn't even support it.

Unicode only supports 1,111,998: 17 planes × 65,536 characters per plane - 2048 surrogates - 66 noncharacters. See this answer for more information. 1.11 Million code points, is far less than 1.19 Million code points.

StackExchange Database Administrators Q#164641, answer score: 4