"Tim Hart" <tjhart@xxxxxxx> 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
