On Sun, Jan 13, 2013 at 4:43 PM, Tom Lane <t...@sss.pgh.pa.us> wrote:
> Gurjeet Singh <singh.gurj...@gmail.com> writes: > > Can somebody explain why a standalone count(*) returns 1? > > postgres=# select count(*); > > count > > ------- > > 1 > > (1 row) > > The Oracle equivalent of that would be "SELECT count(*) FROM dual". > Does it make more sense to you thought of that way? > For a user, Oracle's case makes perfect sense, since the command is querying a single-row table. In Postgres' case, there's nothing being queried, so the result's got to be either 0 or NULL. > > > I agree it's an odd thing for someone to query, but I feel it should > return > > 0, and not 1. > > For that to return zero, it would also be necessary for "SELECT 2+2" > to return zero rows. Which would be consistent with some views of the > universe, but not particularly useful. Another counterexample is > > regression=# select sum(42); > sum > ----- > 42 > (1 row) > > which by your argument would need to return NULL, since that would be > SUM's result over zero rows. > Hmm.. Now that you put it that way, I agree it's a useful feature, or shall I say, a quirk with useful side effect. -- Gurjeet Singh http://gurjeet.singh.im/
