Creating a 'SET' type
Hi,
I am trying to emulate MySQL's SET type, by creating a new postgresql type.
However, is it possible to create a type that has different parameters
wherever it is used.
For instance - the varchar type takes as a parameter the max characters in
the field. Although there is only one varchar type, it has different
properties depending on whether or not it is varchar(5) or varchar(20).
I wish to be able to declare:
bitset('LOW','MEDIUM','HIGH') // Not sure of exact syntax
Internally stored as an int4.
The trouble is in writing the in and out functions. They need to be able to
store a list of token names in order to recreate the comma delimited list of
tokens from the internal bitset, and vice versa...
Any help?
Thanks,
Chris
--
Christopher Kings-Lynne
Family Health Network (ACN 089 639 243)
"Christopher Kings-Lynne" <chriskl@familyhealth.com.au> writes:
However, is it possible to create a type that has different parameters
wherever it is used.
For instance - the varchar type takes as a parameter the max characters in
the field. Although there is only one varchar type, it has different
properties depending on whether or not it is varchar(5) or varchar(20).
Right now, that support is hard-wired into the parser for each such type
(and there aren't many). It might be interesting to look at what it
would take to make a generalized mechanism whereby a type name could
accept parameters, with a type-specific routine being responsible for
reducing the parameters down to a typmod value. One problem you'd run
into, I think, is creation of parsing ambiguities --- is NUMERIC(9,2)
a type specification, or a function call? Right now it's a type spec
because NUMERIC is a keyword in the grammar, but that won't do for an
extensible mechanism.
regards, tom lane