Hi,
Merlin Moncure wrote:
On Thu, Apr 24, 2008 at 3:01 PM, Tino Wildenhain <tino@xxxxxxxxxxxxx> wrote:
Merlin Moncure wrote:
I think you're being a little too hard on enums here. I was actually
in the anti-enum camp until it was demonstrated to me (and in my own
testing) that using enum for natural ordering vs. fielding the
ordering of the type out to a join is can be a huge win in such cases
where it is important. Relational theory is all well and good, but in
practical terms things like record size, index size, and query
performance are important.
Uhm. Sorry what? Can you demonstrate this particular use?
When I first saw discussion about enumns I kinda hoped they
will be implemented as kind of macro to really map to a table.
But here you go. I'm still looking for a good example to
demonstrate the usefullness of enums (same for arrays for that
matter)
You must not be aware that enums are naturally ordered to make that
statement. Suppose your application needs to order a large table by
a,b,c where b is the an 'enum' type of data. With an enum, the order
is inlined into the key order, otherwise it's out of line, meaning
your you key is larger (enum is 4 bytes, varchar is guaranteed to be
larger), and you need to join out to get the ordering position, use a
functional index, or cache it in the main table.
I see, but couldn't you just use int in this case? And map only when
you need the values for display (usually you want it localized anyway)
I agree with disagree with you on arrays. I think they are generally
a bad idea in terms of using them as a column type. However they are
useful passing data to/from functions and back/forth from the client.
Yes of course, I thought of that (wondering why we can't use value
expressions everywhere)
Tino
