On 31.08.2011 09:14, Jeff Davis wrote:
At one point, the question of casting between range types came up. At
first, this seemed like a fairly reasonable suggestion, but now I don't
think I like the semantics.
A normal cast changes between essentially equivalent values in different
domains. For instance 3 as an int4 is equivalent to 3.0 as a numeric.
However, if we take the simple approach with range types and cast the
bounds, we end up with some weird situations.
First, a range is really a set. So if we take '[1,10)'::int4range and
cast that to numrange, we end up moving from a set of exactly 9 elements
to a set of an infinite number of elements. Going the other way is
probably worse.
Sometimes casts are a bit "lossy" and I suppose we could write that off.
But things get weirder when the total order is different (e.g. different
text collations). Then you end up with a completely different set of
values, which doesn't sound like a cast to me at all.
So, I'm leaning toward just not providing any casts from one range type
to another.
Can you only provide casts that make sense, like between int4 and
numeric range types, and leave out the ones that don't?
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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