On 2015-08-12 7:23 PM, Greg Stark wrote:
On Wed, Aug 12, 2015 at 6:18 PM, Marko Tiikkaja <ma...@joh.to> wrote:
Will finish this up for the next CF, unless someone wants to tell me how
stupid this idea is before that.
I'm kind of puzzled what kind of schema would need this.
The first example I could find from our schema was specifying the URL
for a Remote Procedure Call. You can either specify a single request
URI, or you can specify the pieces: protocol, host, port, path. So the
constraints look roughly like this:
CHECK ((fulluri IS NULL) <> (protocol IS NULL)),
CHECK ((protocol IS NULL) = ALL(ARRAY[host IS NULL, port IS NULL,
path IS NULL]))
Obviously the second one would be much prettier with count_nulls().
The other example is an OOP inheritance-like schema where an object
could be one of any X number of types. You could write that:
CHECK ((a IS NULL)::int + (b IS NULL)::int + (c IS NULL)::int) = 1)
or just:
CHECK (count_nulls(a,b,c) = 1)
The first example could be redesigned with three tables, but that seems
like a cure worse than the disease.
.m
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