I figured out that I need to use the function CHR to enter supplementary unicode characters (code points > FFFF, i.e. planes 1 - F), e.g.
insert into unicode(id, string) values(100, CHR(128120)); -- a mojo character, https://unicodelookup.com/#0x1f478/1
insert into unicode(id, string) values(101, CHR(128121)); -- another mojo
insert into unicode(id, string) values(102, CHR(119071)); -- musical symbol g clef ottava alta
insert into unicode(id, string) values(103, CHR(155648)); -- a very infrequently used Chinese character
insert into unicode(id, string) values(104, CHR(155649)); -- another very infrequently used Chinese character
the parameters are decimal representation of the code point values, e.g. 128120 is the decimal value of 1f478
The format U&'\03B1' only works for chars between 0000 - FFFF
When entered with CHR(), PostgreSQL gets their char_length() correctly, so does substring() function.
Thank you all for help.
James
On Wed, Dec 21, 2016 at 8:31 AM, Tom Lane <tgl@xxxxxxxxxxxxx> wrote:
Vick Khera <vivek@xxxxxxxxx> writes:
> On Wed, Dec 21, 2016 at 2:56 AM, Kyotaro HORIGUCHI <
> horiguchi.kyotaro@xxxxxxxxxx.jp > wrote:
>> A PostgreSQL database with encoding=UTF8 just accepts the whole
>> range of Unicode, regardless that a character is defined for the
>> code or not.
> Interesting... when I converted my application and database to utf8
> encoding, I discovered that Postgres is picky about UTF-8. Specifically the
> UTF-8 code point 0xed 0xa0 0x8d which maps to UNICODE code point 0xd80d.
> This looks like a proper character but in fact is not a defined character
> code point.
Well, we're picky to the extent that RFC 3629 tells us to be picky:
http://www.faqs.org/rfcs/rfc3629.html
The case you mention is rejected because it would be half of a UTF16
"surrogate pair", which should not be used in any Unicode representation
other than UTF16; if we allowed it then there would be more than one way
to represent the same Unicode code point, which is undesirable for a lot
of reasons.
> So I think when you present an actual string of UTF8 encoded characters,
> Postgres does refuse characters unknown. However, as you observe, inserting
> the unicode code point directly does not produce an error:
> insert into unicode(id, string) values(1, U&'\d80d');
> INSERT 0 1
Hm. I think that's a bug. The lexer does know that \d80d is half of a
surrogate pair, and it expects the second half to come next. If you
supply something that isn't the second half of a surrogate pair, you
get an error as expected:
u8=# insert into unicode(id, string) values(1, U&'\d80dfoo');
ERROR: invalid Unicode surrogate pair at or near "foo'"
LINE 1: insert into unicode(id, string) values(1, U&'\d80dfoo');
^
But it looks like if you just end the string after the first half of a
surrogate, it just drops the character without complaint. Notice that
what got inserted was a zero-length string, not U+D08D:
u8=# select *, length(string) from unicode;
id | string | length
----+--------+--------
1 | | 0
(1 row)
I'd have expected a syntax error along the line of "incomplete Unicode
surrogate pair". Peter, I think this was your code to begin with ---
was it intentional to not raise error here, or is that an oversight?
regards, tom lane
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