Re: Content for talk on Postgres Type System at PostgresConf

On 28 Feb 2024, at 17:08, Guyren Howe <guyren(at)gmail(dot)com> wrote:
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> I am to talk about Postgres’s type system at PGConf:
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> https://postgresconf.org/conferences/2024/program/proposals/postgres-s-type-system
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> I picked the issue because I think it’s poorly understood, greatly under-discussed, and an excellent way to empower postgres users.
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> I am reasonably conversant with the issue. I’m not looking for others to write the talk for me, but in order to make the best talk I can, I’m asking:
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> What would you want to see in such a talk?
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> I’m planning on covering:
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> - The built-in types that are underused and their advantages (eg inet)
> - domains
> - such things as details of arrays including multidimensional arrays
> - user-defined types, their relationship to tables, and generally how to use them
>
> I would spend most of the time discussing ways to make effective use of types. Some examples:
> - defining functions of rows so the table can be used kind of like a set of objects (including the dot notation for invoking functions)
> - using UDFs to make code clearer eg if you have an idiosyncratic functional index, define it using a function of the row, so it’s easy to get right when querying
> - using UDFs as a kind of better domain. eg differentiating imperial from metric units by requiring an explicit constructor, not just accepting any old number
>
> I would mention enumerated types, although I’m inclined to advise that their inflexibility (eg can’t delete or rearrange them) means that a related table is probably better (I’d be delighted to be proved wrong).
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> Custom Range Types are an interesting feature, but I can’t think of a good use case. Any good examples?
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> Automatic casting is a feature I’m aware of, but I’d be interested in any cool use cases.
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>
> Anything I’m missing? Any existing good discussions of the subject?

Any gotchas about user defined types or arrays? I was only planning on discussing simple user defined types, without going into writing the optional features in C.

What is worth saying about custom range types? What even would be a good use case? A range of strings or ip address ranges, something like that, I suppose?

Is there a good case for enumerations versus a fk to a table? I guess if you’re sure you won’t need to change the values in the enumeration? Days of the week, that sort of thing.