For my own amusement I'm reading the sql 92 spec about character sets.
There are some concepts that are a bit difficult that maybe someone can
explain for me:
character set
character repertoire
for example in 4.2.1 it says:
A character set is described by a character set descriptor. A
character set descriptor includes:
- the name of the character set or character repertoire,
- if the character set is a character repertoire, then the name
of the form-of-use,
- an indication of what characters are in the character set, and
- the name of the default collation of the character set.
What I have understod so far is that form-of-use is the encoding. So if
the character set is UNICODE then the form-of-use could be UTF-8, UTF-16
and so on.
The character repertoire however I don't have an intuition about it all.
Then we have this little section:
The <implementation-defined character repertoire name> SQL_TEXT
specifies the name of a character repertoire and implied form-of-
use that can represent every character that is in <SQL language
character> and all other characters that are in character sets
supported by the implementation.
Had unicode been a superset of all character sets, then one could just
have used unicode for SQL_TEXT. Exactly how do we create a character
repertoire that can store any character from any character set.. Storing
the character set for each character is not such a cool thing to do
even if it would work :-)
SQL_ASCII in pg is similar, it's basically a number of bytes. But the spec
seems to say that one should be able to count the characters as well (not
the bytes) so SQL_ASCII is not the same as SQL_TEXT.
ps. This is not me volunteering to implement all this :-)
--
/Dennis Björklund
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TIP 8: explain analyze is your friend
