On Tue, Jun 14, 2016 at 8:47 AM, James K. Lowden <jklow...@schemamania.org>
wrote:
> On Mon, 13 Jun 2016 19:11:29 +0000
> "Drago, William @ CSG - NARDA-MITEQ" <william.dr...@l-3com.com> wrote:
>
> > I need UNIQUE(B, C) only when E=0.
>
> A conditional constraint is evidence that you have two kinds of things
> represented in one table: those E=0 types that are identified by {B,C},
> and the rest. They're represented in a single table because they
> seem to have the same columns, although the E=0 types don't need an E
> column.
>
> A better solution might be to separate the two types into to two
> tables, each with its own constraints, and use a UNION to represent
> them as one.
>
> --jkl
>
I was thinking the same thing, but couldn't phrase it as well as you did.
But I have this unusual(?) habit of liking to do things "by the book",
which in this case tends to be "Database Design & Relational Theory" and
"SQL and Relational Theory", both by Dr. C. J. Date
. Also tend to be more a theorist than an actual "real world"
practitioner. I.e. I favor design over performance more than I should.
--
"Pessimism is a admirable quality in an engineer. Pessimistic people check
their work three times, because they're sure that something won't be right.
Optimistic people check once, trust in Solis-de to keep the ship safe, then
blow everyone up."
"I think you're mistaking the word optimistic for inept."
"They've got a similar ring to my ear."
From "Star Nomad" by Lindsay Buroker:
Maranatha! <><
John McKown
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