Martijn van Oosterhout <kleptog@svana.org> writes:
> On Tue, Jan 25, 2005 at 02:31:40PM -0500, Tom Lane wrote:
>> AFAICS this could easily be implemented as a user-defined type, along
>> the lines of
>> CREATE TYPE measurement AS (value double, units text);
>> and if you want to constrain a particular column to contain only one
>> value of units, use CHECK.
> I've tried this but I can't work out how to make it work. For composite
> types you can't specify input and output functions.
No, but as of 8.0 you don't really need them, assuming that you don't
mind some parentheses around your output.
regression=# CREATE TYPE measurement AS (value float, units text);
CREATE TYPE
regression=# select cast( (5,'a') as measurement);
row
-------
(5,a)
(1 row)
Or you can implement it as a scalar type if you really want to define
your own I/O functions.
regards, tom lane
