hvorfor er det unødvendig med - Universitetet i oslo...select*...

fdb=> \d film! Table "public.film"! Column | Type | Modifiers !----------+---------+-----------! filmid | integer | ! title | text | not null! prodyear | integer | !Indexes:! "filmpkey" UNIQUE CONSTRAINT, btree (filmid)! "filmtitleindex" btree (title)! "filmyearindex" btree (prodyear)!Foreign-key constraints:! "filmfkey" FOREIGN KEY (filmid) REFERENCES filmitem(filmid)!!!!!select count (filmid)!from film; -- hvorfor er det unødvendig med distinct filmid ?!

fdb=> \d filmcountry! Table "public.filmcountry"! Column | Type | Modifiers !---------+---------+-----------! filmid | integer | ! country | text | !Indexes:! "filmcountrypkey" UNIQUE CONSTRAINT, btree (filmid, country)! "filmcountryfilmidindex" btree (filmid)!Foreign-key constraints:! "filmcountryfkey" FOREIGN KEY! (filmid) REFERENCES filmitem(filmid)!!!!!!!select count (distinct filmid)!from filmcountry; -- hvorfor er distinct nødvendig her?!!

select * from Film F natural join Filmcountry C

( filmid, 8tle, prodyear, country )

F.filmid = C.filmid

( F.filmid, 8tle, prodyear, C.filmid, country )

F.filmid = C.filmid

Et tuppel fra F x C (kartesisk produkt) har disse a6ribu6ene:

F.filmid is not null and C.filmid is null

C.filmid is not null and F.filmid is null F.filmid = C.filmid

F.filmid is not null and C.filmid is not null and F.filmid <> C.filmid F.filmid = C.filmid

F.filmid is not null and C.filmid is not null and F.filmid <> C.filmid

filmid | title | prodyear !---------+------------+----------! 29000 | Armageddon | 1998! 217739 | Armageddon | 1999! 271692 | Armageddon | 1994! 334412 | Armageddon | 1977! 432538 | Armageddon | 1923! 432554 | Armageddon | 1962! 432570 | Armageddon | 1969! 831068 | Armageddon | 1997! 1969660 | Armageddon | 1998! 2728636 | Armageddon | 1989! 2984924 | Armageddon | 1997!!

natural join

Hengetupler

Hengetupler har en verdi i joinaCribuCet som ikke finnes i tabellen det joines med

De blir ikke med i F natural join C

C.filmid is not null and F.filmid is null

F.filmid = C.filmid

hengetupler hengetupler

Select * from Film F full outer join Filmcountry C on F.filmid=C.filmid

432570 | Armageddon | 1969 | 432570 | Canada

2984924 | Armageddon | 1997 | | |

filmid | title | prodyear | filmid | country !---------+-----------------+----------+---------+--------------! 29000 | Armageddon | 1998 | 29000 | USA! | | | 43329 | Kosovo! | | | 79787 | Kosovo! | | | 123751 | Kosovo! 175640 | Migjeni | 1990 | 175640 | Kosovo! 217739 | Armageddon | 1999 | 217739 | USA! 271692 | Armageddon | 1994 | | ! 334412 | Armageddon | 1977 | | ! | | | 381154 | Kosovo! 432538 | Armageddon | 1923 | 432538 | UK! 432554 | Armageddon | 1962 | 432554 | Soviet Union! 432570 | Armageddon | 1969 | 432570 | Canada! 629179 | Etjet e Kosovës | 2006 | 629179 | Kosovo! 706983 | Kulla | 1991 | 706983 | Kosovo! 831068 | Armageddon | 1997 | | ! 1969660 | Armageddon | 1998 | | ! 2728636 | Armageddon | 1989 | | ! 2984924 | Armageddon | 1997 | | ! 3790202 | Kukumi | 2005 | 3790202 | Kosovo! 4867338 | Një lindje | 1973 | 4867338 | Kosovo!

F.filmid| title | prodyear | C.filmid| country !---------+-----------------+----------+---------+--------------! 29000 | Armageddon | 1998 | 29000 | USA! | | | 43329 | Kosovo! | | | 79787 | Kosovo! | | | 123751 | Kosovo! 175640 | Migjeni | 1990 | 175640 | Kosovo! 217739 | Armageddon | 1999 | 217739 | USA! 271692 | Armageddon | 1994 | | ! 334412 | Armageddon | 1977 | | ! | | | 381154 | Kosovo!

full outer join

select * from Film F full outer join Filmcountry C on F.filmid=C.filmid

F.filmid| title | prodyear | C.filmid| country !---------+-----------------+----------+---------+--------------! 29000 | Armageddon | 1998 | 29000 | USA! | | | 43329 | Kosovo! | | | 79787 | Kosovo! | | | 123751 | Kosovo! 175640 | Migjeni | 1990 | 175640 | Kosovo! 217739 | Armageddon | 1999 | 217739 | USA! | | | 381154 | Kosovo!

F.filmid = C.filmid

F.filmid| title | prodyear | C.filmid| country !---------+-----------------+----------+---------+--------------! 29000 | Armageddon | 1998 | 29000 | USA! 175640 | Migjeni | 1990 | 175640 | Kosovo! 217739 | Armageddon | 1999 | 217739 | USA!

F.filmid = C.filmid

inner join

F.filmid = C.filmid

inner join

select * from Film F inner join Filmcountry C on F.filmid=C.filmid

F.filmid = C.filmid

inner join

select * from Film F inner join Filmcountry C on F.filmid=C.filmid

sammenlign med select * from Film natural join Filmcountry

F.filmid = C.filmid

F.filmid| title | prodyear | C.filmid| country !---------+-----------------+----------+---------+--------------! 29000 | Armageddon | 1998 | 29000 | USA! 175640 | Migjeni | 1990 | 175640 | Kosovo! 217739 | Armageddon | 1999 | 217739 | USA! 271692 | Armageddon | 1994 | | ! 334412 | Armageddon | 1977 | | !

F.filmid = C.filmid

leW outer join

F.filmid = C.filmid

select * from Film F leW outer join Filmcountry C on F.filmid=C.filmid

leW outer join

right outer join

select * from Film F right outer join Filmcountry C on F.filmid=C.filmid

right outer join

F.filmid| title | prodyear | C.filmid| country !---------+-----------------+----------+---------+--------------! | | | 43329 | Kosovo! | | | 79787 | Kosovo! | | | 123751 | Kosovo! 271692 | Armageddon | 1994 | | ! 334412 | Armageddon | 1977 | | ! | | | 381154 | Kosovo!

F.filmid = C.filmid

hvorfor er det unødvendig med - Universitetet i oslo...select*...

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