2009/9/11 Stephen Frost <sfr...@snowman.net>: >>>> Postgres has a hstore data type which seems well suited for passing >>>> key/value option pairs... >> >> Quite apart from any other reason, it is not builtin, so there is no way >> that any builtin thing can use it. > > Clearly, that's fixable.. I think it's an interesting concept, but I > don't know that I'd advocate it (using hstore for this in some way).
Unless I'm missing something, which is possible, this whole line of conversation is based on a misunderstanding. Data types, like hstore, are things that have input/output functions, index methods, and on-disk representations. In-memory data structures require none of these things, and can use techniques not suitable for on-disk representations, such as pointers. The parser already has an object called a DefElem which is well-suited for exactly the kind of option handling we're talking about here, and hstore would not be, not only because it's the wrong kind of object (a data type rather than an in-memory data structure), but because a DefElem can do things that hstore can't, like store as the associated value a list of parse nodes. The original reference to hstore was a suggestion that it might be possible to pass an hstore argument to COPY rather than having to build up a command string and pass it to EXECUTE. That may or may not be a useful innovation - personally, I tend to think not - but it seems to me that it would require COPY to execute an arbitrary subquery and use the results as options. We have no other commands that work that way to my knowledge, but beyond that, Pierre Frédéric Caillaud seemed to be suggesting this would be an "easier" way to implement an options syntax. Integrating hstore into core and then making COPY able to execute a subquery to get its options is certainly not easier than a straightforward grammar modification; it's taking a small project and turning it into several big ones. ...Robert -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
