Re: Alter or rename enum value

On Friday, March 25, 2016, Andrew Dunstan <andrew(at)dunslane(dot)net> wrote:

>
> On 03/25/2016 04:13 AM, Matthias Kurz wrote:
>
>>
>> Hopefully at the commitfest at least the transaction limitation
>> will/could be tackled - that would help us a lot already.
>>
>>
> I don't believe anyone knows how to do that safely. Enums pose special
> problems here exactly because unlike all other types the set of valid
> values is mutable.
>

Yeah, I'm not sure there is much blue sky here as long as the definition of
an enum is considered system data. It probably needs to be altered so that
a user can create a table of class enum with a known layout that PostgreSQL
can rely upon to perform optimizations and provide useful behaviors - at
least internally. The most visible behavior being displaying the label
while ordering using its position.

The system, seeing a data type of that class, would have an implicit
reference between columns of that type and the source table.
You have to use normal cascade update/delete/do-nothing while performing
DML on the source table.

In some ways it would be a specialized composite type, and we could
leverage that to you all the syntax available for those - but without
having a different function for each differently named enum classed table
since they all would share a common structure, differing only in name. But
the tables would be in user space and not a preordained relation in
pg_catalog. Maybe require they all inherit from some template but empty
table...

David J.