Ok. This behaviour is documented here: https://www.sqlite.org/lang_expr.html#booleanexpr
--- The fact that there's a Highway to Hell but only a Stairway to Heaven says a lot about anticipated traffic volume. >-----Original Message----- >From: sqlite-users [mailto:sqlite-users- >boun...@mailinglists.sqlite.org] On Behalf Of Keith Medcalf >Sent: Saturday, 1 December, 2018 12:45 >To: SQLite mailing list >Subject: [sqlite] is True (was: geopoly_contains_point(P, X, Y) doc >is overly modest) > > >On Saturday, 1 December, 2018 12:23, Richard Hipp <d...@sqlite.org> >wrote" > >>On 12/1/18, Keith Medcalf <kmedc...@dessus.com> wrote: > >>>>Maybe it should say 'Non-Zero' or 'Greater than Zero' rather than >>>>true, since true, as a symbol, as a special value. > >>> Yes and no, True and False is SQLite work as one would expect >>> (assuming that one is a programmer is a language that behaves >>> as the underlying hardware (CPU) behaves). > >> Yeah, but Mr. Damon is probably right that the documentation should >> be more precise. So I have now updated it. > >I concur. > >There is however a slight anomaly with how the "is True" test works >that has to do with how type affinities work such that "is True" does >not work entirely as one would expect from a machine perspective. >Presently the LHS of an "is True" is not NUMERIC it is converted to >NUMERIC before the "is True" expression is evaluated, rather than "is >True" being a test for any bits being 1 the LHS. > >This means that ('' is true) evaluates to 0, which is expected, since >there are no bits set in the value on the LHS (it also by >happenstance converts to 0 in numeric affinity). However (select 'a' >is true) evaluates to 0. This is incorrect because there are bits >set in the value on the LHS. However if the LHS can be cast to >numeric the test works as expected: > >sqlite> select '' is true; >0 >sqlite> select 'a' is true; >0 >sqlite> select '1' is true; >1 >sqlite> select '2' is true; >1 >sqlite> select '.1' is true; >1 >sqlite> select '-1' is true; >1 >sqlite> select '-0.1' is true; >1 >sqlite> select '0' is true; >0 >sqlite> select '0.0' is true; >0 >sqlite> select '0.1' is true; >1 > >I don't recall if this is documented anywhere but one should expect >(at least I would expect) that ('a' is true) should evaluate as 1, >not 0, since there are bits set in the value on the LHS. > > > > > >_______________________________________________ >sqlite-users mailing list >sqlite-users@mailinglists.sqlite.org >http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users _______________________________________________ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
