"Tim Hart" <tjhart@mac.com> writes:
> I've reviewed the PostgreSQL documentation on user defined data types. It
> seems that data types that can't be ordered or compared for equality would
> be bad candidates. After all, if a data type can't be indexed or used in a
> where clause, what value does a custom type bring over a binary or textual
> representation?
Well, the possibility of error-checking for bad values might alone
justify a custom type, depending on what you're doing. A type with no
support beyond the required I/O functions could offer that.
But it's kinda hard to imagine a datatype in which there is no
meaningful way to define equality ...
regards, tom lane