Thanks for the responses. Just a brain error. Not sure what I was
thinking :)
On Tue, May 15, 2018 at 6:55 PM R Smith <ryansmit...@gmail.com> wrote:
>
> On 2018/05/16 1:25 AM, Mark Wagner wrote:
> > OK, at the risk of exposing my lack of edification...
>
> Sometimes you pay the price for taking a risk. :)
>
> > create table t (k integer primary key, s text UNIQUE);
>
> Did you by any chance assume the "UNIQUE" constraint to cover both the
> fields k and s? It applies of course only to s here. If you wanted it to
> apply to both, the schema should read:
> create table t(k integer primary key, s text, unique(k,s) );
>
> (I'm just trying to guess at what caused the confusion - even if you do
> change to this schema, the uniqueness constraint will pass even better
> than before, since the primary key is by definition unique and
> automatically increments, so any key in which it appears MUST also be
> unique for every value in it, even if you added 'bar' ten times in a
> row, it will never fail.)
>
> > insert into t (s) values ("foo");
> > insert into t (s) values ("bar");
> > select * from t;
> > k s
> > ---------- ----------
> > 1 foo
> > 2 bar
>
> foo and bar here (which should be quoted like 'foo' and 'bar' by the
> way, double-quotes are for identifiers) are very unique, so cannot
> possibly constitute a uniqueness violation.
>
> >
> > Adding to my confusion is this:
> >
> > insert into t values (3, "bar");
> > Error: UNIQUE constraint failed: t.s
>
> whereas 'bar' here definitely is not unique (there is already a 'bar' in
> there) and thus fails.
>
> I've always found the higher level languages to be slightly less than
> intuitive, since they try to "read like English", except the language is
> nuanced and often what something seems to mean in English is not what it
> really means in the computed sense. That means that a statement fragment
> like UNIQUE needs as much documentation as, for instance, the lower
> level assembly language MOV command, if not more, because MOV left you
> with zero assumptions, you had to check the docs to see what it did, and
> even then, it delightfully did the very minimum.
>
>
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