Обсуждение: Existential quantifier

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Existential quantifier

От
Dag-Erling Smørgrav
Дата:
Consider the attached schema (filmstars.sql), which is a poorly designed
database of films and actors.  The following query gives me a list of
films in which either Charlie or Martin Sheen starred:

select fs.film.title, fs.film.year
  from fs.film left join fs.star on fs.film.id = fs.star.film
  where fs.star.last = 'Sheen'
  group by fs.film.title, fs.film.year;

Is there a way to do this without the "group by" clause?

DES
--
Dag-Erling Smørgrav - des@des.no

drop schema fs cascade;

create schema fs;

create table fs.film (
  id serial not null primary key,
  title varchar not null unique,
  year integer not null
);

create table fs.star (
  id serial not null primary key,
  film integer not null references fs.film(id),
  last varchar not null,
  first varchar not null,
  unique (film, last, first)
);

insert into fs.film(title, year) values ('Apocalypse Now', 1979);
insert into fs.star(film, last, first)
  select id, 'Sheen', 'Martin' from fs.film where title = 'Apocalypse Now';
insert into fs.star(film, last, first)
  select id, 'Brando', 'Marlon' from fs.film where title = 'Apocalypse Now';
insert into fs.star(film, last, first)
  select id, 'Duvall', 'Robert' from fs.film where title = 'Apocalypse Now';
insert into fs.star(film, last, first)
  select id, 'Ford', 'Harrison' from fs.film where title = 'Apocalypse Now';

insert into fs.film(title, year) values ('Blade Runner', 1982);
insert into fs.star(film, last, first)
  select id, 'Ford', 'Harrison' from fs.film where title = 'Blade Runner';
insert into fs.star(film, last, first)
  select id, 'Young', 'Sean' from fs.film where title = 'Blade Runner';
insert into fs.star(film, last, first)
  select id, 'Hauer', 'Rutger' from fs.film where title = 'Blade Runner';
insert into fs.star(film, last, first)
  select id, 'Hannah', 'Daryl' from fs.film where title = 'Blade Runner';

insert into fs.film(title, year) values ('Platoon', 1986);
insert into fs.star(film, last, first)
  select id, 'Sheen', 'Charlie' from fs.film where title = 'Platoon';
insert into fs.star(film, last, first)
  select id, 'Dafoe', 'Willem' from fs.film where title = 'Platoon';
insert into fs.star(film, last, first)
  select id, 'Berenger', 'Tom' from fs.film where title = 'Platoon';

insert into fs.film(title, year) values ('Wall Street', 1987);
insert into fs.star(film, last, first)
  select id, 'Douglas', 'Michael' from fs.film where title = 'Wall Street';
insert into fs.star(film, last, first)
  select id, 'Sheen', 'Charlie' from fs.film where title = 'Wall Street';
insert into fs.star(film, last, first)
  select id, 'Hannah', 'Daryl' from fs.film where title = 'Wall Street';
insert into fs.star(film, last, first)
  select id, 'Sheen', 'Martin' from fs.film where title = 'Wall Street';

Re: Existential quantifier

От
Stephan Szabo
Дата:
On Sat, 10 Oct 2009, [utf-8] Dag-Erling Smørgrav wrote:

> Consider the attached schema (filmstars.sql), which is a poorly designed
> database of films and actors.  The following query gives me a list of
> films in which either Charlie or Martin Sheen starred:
>
> select fs.film.title, fs.film.year
>   from fs.film left join fs.star on fs.film.id = fs.star.film
>   where fs.star.last = 'Sheen'
>   group by fs.film.title, fs.film.year;
>
> Is there a way to do this without the "group by" clause?

Not at all tested as I don't have access to my db right now, but I think
something like one of these would work:

select fs.film.title, fs.film.yearfrom fs.filmwhere exists(select 1 from fs.star where fs.film.id = fs.star.film and
fs.star.last= 'Sheen'); 

select fs.film.title, fs.film.yearfrom fs.filmwhere fs.film.id in (select fs.star.film where fs.star.last = 'Sheen');

Re: Existential quantifier

От
Richard Albright
Дата:
you could use distinct on

select distinct on (fs.film.title, fs.film.year ) title, year
from fs.film left join fs.star on fs.film.id = fs.star.film where fs.star.last = 'Sheen';

On Sat, 2009-10-10 at 00:53 +0200, Dag-Erling Smørgrav wrote:
> Consider the attached schema (filmstars.sql), which is a poorly designed
> database of films and actors.  The following query gives me a list of
> films in which either Charlie or Martin Sheen starred:
> 
> select fs.film.title, fs.film.year
>   from fs.film left join fs.star on fs.film.id = fs.star.film
>   where fs.star.last = 'Sheen'
>   group by fs.film.title, fs.film.year;
> 
> Is there a way to do this without the "group by" clause?
> 
> DES
> plain text document attachment (filmstars.sql)
> drop schema fs cascade;
> 
> create schema fs;
> 
> create table fs.film (
>   id serial not null primary key,
>   title varchar not null unique,
>   year integer not null
> );
> 
> create table fs.star (
>   id serial not null primary key,
>   film integer not null references fs.film(id),
>   last varchar not null,
>   first varchar not null,
>   unique (film, last, first)
> );
> 
> insert into fs.film(title, year) values ('Apocalypse Now', 1979);
> insert into fs.star(film, last, first)
>   select id, 'Sheen', 'Martin' from fs.film where title = 'Apocalypse Now';
> insert into fs.star(film, last, first)
>   select id, 'Brando', 'Marlon' from fs.film where title = 'Apocalypse Now';
> insert into fs.star(film, last, first)
>   select id, 'Duvall', 'Robert' from fs.film where title = 'Apocalypse Now';
> insert into fs.star(film, last, first)
>   select id, 'Ford', 'Harrison' from fs.film where title = 'Apocalypse Now';
> 
> insert into fs.film(title, year) values ('Blade Runner', 1982);
> insert into fs.star(film, last, first)
>   select id, 'Ford', 'Harrison' from fs.film where title = 'Blade Runner';
> insert into fs.star(film, last, first)
>   select id, 'Young', 'Sean' from fs.film where title = 'Blade Runner';
> insert into fs.star(film, last, first)
>   select id, 'Hauer', 'Rutger' from fs.film where title = 'Blade Runner';
> insert into fs.star(film, last, first)
>   select id, 'Hannah', 'Daryl' from fs.film where title = 'Blade Runner';
> 
> insert into fs.film(title, year) values ('Platoon', 1986);
> insert into fs.star(film, last, first)
>   select id, 'Sheen', 'Charlie' from fs.film where title = 'Platoon';
> insert into fs.star(film, last, first)
>   select id, 'Dafoe', 'Willem' from fs.film where title = 'Platoon';
> insert into fs.star(film, last, first)
>   select id, 'Berenger', 'Tom' from fs.film where title = 'Platoon';
> 
> insert into fs.film(title, year) values ('Wall Street', 1987);
> insert into fs.star(film, last, first)
>   select id, 'Douglas', 'Michael' from fs.film where title = 'Wall Street';
> insert into fs.star(film, last, first)
>   select id, 'Sheen', 'Charlie' from fs.film where title = 'Wall Street';
> insert into fs.star(film, last, first)
>   select id, 'Hannah', 'Daryl' from fs.film where title = 'Wall Street';
> insert into fs.star(film, last, first)
>   select id, 'Sheen', 'Martin' from fs.film where title = 'Wall Street';
-- 
Rick Albright
Senior Quantitative Analyst
Insiderscore LLC
ralbright@insiderscore.com

Re: Existential quantifier

От
Dag-Erling Smørgrav
Дата:
Richard Albright <ralbright@insiderscore.com> writes:
> you could use distinct on
>
> select distinct on (fs.film.title, fs.film.year ) title, year
> from fs.film left join fs.star on fs.film.id = fs.star.film
>   where fs.star.last = 'Sheen';

Thanks, I didn't know about "distinct on".  This version uses the
primary (surrogage) key:

select distinct on (fs.film.id) fs.film.title, fs.film.year from fs.film left join fs.star on fs.film.id = fs.star.film
wherefs.star.last = 'Sheen'; 

DES
--
Dag-Erling Smørgrav - des@des.no

Re: Existential quantifier

От
Dag-Erling Smørgrav
Дата:
Stephan Szabo <sszabo@megazone.bigpanda.com> writes:
> Not at all tested as I don't have access to my db right now, but I think
> something like one of these would work:
>
> select fs.film.title, fs.film.year
>  from fs.film
>  where exists(select 1 from fs.star where fs.film.id = fs.star.film
>   and fs.star.last = 'Sheen');

Ah, that was exactly what I was looking for.

> select fs.film.title, fs.film.year
>  from fs.film
>  where fs.film.id in (select fs.star.film where fs.star.last = 'Sheen');

ITYM

select fs.film.title, fs.film.yearfrom fs.filmwhere fs.film.id in (  select fs.star.film from fs.star where
fs.star.last= 'Sheen'); 

(missing FROM)

DES
--
Dag-Erling Smørgrav - des@des.no

Re: Existential quantifier

От
Stephan Szabo
Дата:
On Sat, 10 Oct 2009, [utf-8] Dag-Erling Smørgrav wrote:

> Stephan Szabo <sszabo@megazone.bigpanda.com> writes:
> > Not at all tested as I don't have access to my db right now, but I think
> > something like one of these would work:
> >
> > select fs.film.title, fs.film.year
> >  from fs.film
> >  where exists(select 1 from fs.star where fs.film.id = fs.star.film
> >   and fs.star.last = 'Sheen');
>
> Ah, that was exactly what I was looking for.
>
> > select fs.film.title, fs.film.year
> >  from fs.film
> >  where fs.film.id in (select fs.star.film where fs.star.last = 'Sheen');
>
> ITYM
>
> select fs.film.title, fs.film.year
>  from fs.film
>  where fs.film.id in (
>    select fs.star.film from fs.star where fs.star.last = 'Sheen'
>  );
>
> (missing FROM)

Yeah, that'd be necessary. You might want to try them on a realistic data
set to see how the various options are planned.