Re: DOMAINs and CASTs
От | Gelman |
---|---|
Тема | Re: DOMAINs and CASTs |
Дата | |
Msg-id | 0177D96950FE45E6B6C325D3A67E91E1@Igel01 обсуждение исходный текст |
Ответ на | Re: DOMAINs and CASTs (Darren Duncan <darren@darrenduncan.net>) |
Список | pgsql-hackers |
----- Original Message ----- From: "Darren Duncan" <darren@darrenduncan.net> To: "Jaime Casanova" <jaime@2ndquadrant.com> Cc: "PostgreSQL-development" <pgsql-hackers@postgresql.org> Sent: Saturday, May 14, 2011 9:46 PM Subject: Re: [HACKERS] DOMAINs and CASTs > Darren Duncan wrote: >> I think it would be best that the generic cast syntax only be useable for >> casts defined on the base type, and if you want a domain-specific one you >> should use the function syntax such as your datetime2int(). >> >> That way it is easier for users to predict what behavior will occur, and >> implementation will be easier too. > > Replying to myself, I offer another alternative: > > What you ask for is indeed supported, but that if for a given input value > more than one cast applies to it, particularly for 2 overlapping domains, > then which cast is invoked is undefined, so for example the DBMS may just > use the first one it finds. > > It is then up to the user to ensure that when they define casts over > domains that they just define ones that either produce the same outputs > for the same overlapping inputs (the best answer) or they ensure that they > don't overlap in their input domains. > > -- Darren Duncan > > -- > Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-hackers
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