[GENERAL] How well does PostgreSQL 9.6.1 support unicode?
Unicode has evolved from version 1.0 with 7,161 characters released in 1991 to version 9.0 with 128,172 characters released in June 2016. My questions are
- which version of Unicode is supported by PostgreSQL 9.6.1?
- what does "supported" exactly mean? simply store it? comparison? sorting? substring? etc.
Below is a test I did which reveals some unexpected behaviors.
My test database 'gsdb' is using UTF8 encoding, confirmed by
select datname, datcollate, datctype, pg_encoding_to_char(encoding)
from pg_database
where datname = 'gsdb';
which returned UTF8.
Here is a simple test table:
create table unicode (id int, string varchar(100));
Then I insert some unicode characters by referencing their code points in hexadecimal:
/* characters from BMP, 0000 - FFFF */
insert into unicode(id, string) values(1, U&'\0041'); -- 'A'
insert into unicode(id, string) values(2, U&'\00C4'); -- 'A' with umlaut, German
insert into unicode(id, string) values(3, U&'\03B1'); -- Greek letter alpha
insert into unicode(id, string) values(4, U&'\6211'); -- a Chinese character, https://unicodelookup.com/#0x6211/1
insert into unicode(id, string) values(5, U&'\6211\4EEC'); -- a string of two Chinese characters
insert into unicode(id, string) values(6, U&'\30CF'); -- a Japanese character
insert into unicode(id, string) values(7, U&'\306F'); -- a Japanese character
insert into unicode(id, string) values(8, U&'\2B41'); -- https://unicodelookup.com/#0x2b41/1
insert into unicode(id, string) values(9, U&'\2B44'); -- https://unicodelookup.com/#0x2b44/1
insert into unicode(id, string) values(10, U&'\2B50'); -- https://unicodelookup.com/#0x2b50/1
/* Below are unicode characters with code points beyond FFFF, aka planes 1 - F */
insert into unicode(id, string) values(100, U&'\1F478'); -- a mojo character, https://unicodelookup.com/#0x1f478/1
insert into unicode(id, string) values(101, U&'\1F479'); -- another mojo
insert into unicode(id, string) values(102, U&'\1D11F'); -- musical symbol g clef ottava alta
insert into unicode(id, string) values(103, U&'\26000'); -- a very infrequently used Chinese character
insert into unicode(id, string) values(104, U&'\26001'); -- another very infrequently used Chinese character
insert into unicode(id, string) values(105, U&'\26000\26001'); -- a string with 2 Chinese characters in the plane 2
The SELECT below shows what PostgreSQL has recorded:
select id, string,
char_length(string),
octet_length(string),
ascii(string),
substring(string, 1, 1) as firstChar,
ascii(substring(string, 1, 1)) as unicodeInt
from unicode
order by string;
Here are the results:
Observations
- BMP characters (id <= 10)
- they are stored and fetched correctly.
- their lengths in char are correct, although some of them take 3 bytes (id = 4, 6, 7)
- But their sorting order seems to be undefined. Can anyone comment the sorting rules?
- Non-BMP characters (id >= 100)
- they take 2 - 4 bytes.
- Their lengths in character are not correct
- they are not retrieved correctly, judged by the their fetched ascii value (column 5 in the table above)
- substring is not correct
Specifically, the lack of support for emojo characters 0x1F478, 0x1F479 is causing a problem in my application.
My conclusion:
- PostgreSQL 9.6.1 only supports a subset of unicode characters in BMP. Is there any documents defining which subset is fully supported?
Are any configuration I can change so that more unicode characters are supported?
Thanks
James
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