> I've been think this for a while too. What about collation? If we add
> new chaset A and B, and each has 10 collations then we are going to
> have 20 new types? That seems overkill to me.
Well, afaict all of the operations we would ask of a type we will be
required to provide for character sets and collations. So ordering,
conversions, operators, index methods, etc etc are all required. It
*does* seem like a lot of work, but the type system is specifically
designed to do exactly this. Lifting those capabilities out of the type
system only to reimplement them elsewhere seems all trouble with no
upside.
Perhaps the current concept of "binary compatible types" could help
reduce the complexity, if it were made extensible, which it needs
anyway. But in most cases the character set/collation pair is a unique
combination, with a limited set of possibilities for other character
set/collation pairs with equivalent forms of use, which would keep us
from being able to reuse pieces anyway.
For most installations, we would install just those character sets the
installation/database requires, so in practice the database size need
not grow much beyond what it already is. And we could have conventions
on how functions and operators are named for a character set and/or
collation, so we could auto-generate the SQL definitions given an
implementation which meets a template standard.
Hmm, an aside which might be relevant: I've been looking at the
"national character string" syntax (you know, the N'string' convention)
and at the binary and hex string syntax (B'101010' and X'AB1D', as
examples) and would like to implement them in the lexer and parser by
having the string preceded with a type identifier as though they were
something like
NATIONAL CHARACTER 'string'
BIN '101010'
HEX 'AB1D'
where both BIN and HEX result in the *same* underlying data type once
ingested (or at least a reasonable facimile). I won't be allowed to
create two data types with the same type OID, but maybe if I assign them
to be binary compatible then I won't have to flesh out the hex data type
but only provide an input and output function.
- Thomas