如何从多个表中获取所有记录，甚至没有值的记录

Question

So I 've got many tables for a movies database (Films, FilmPersons, Persons, PersonEmails, Roles, FilmGenres, Genres).

I want to output all films that exist with as many information as possible. For example one row would be:

Title | Date | Budget | Actor | Director | Genre |  
Alien | 1923 | 3322 | someActor | someDirector | Scifi

SELECT        Films.Title, Films.Date, Films.Budget, Persons.FirstName, Persons.LastName, Roles.RoleName, Genres.Name 
FROM            Films INNER JOIN
                     FilmPersons ON Films.FilmID = FilmPersons.FilmID INNER JOIN
                     Persons ON FilmPersons.PersonID = Persons.PersonID INNER JOIN
                     Roles ON FilmPersons.RoleID = Roles.RoleID INNER JOIN
                     FilmGenres ON Films.FilmID = FilmGenres.FilmID INNER JOIN
                     Genres ON FilmGenres.GenreID = Genres.GenreID

But the above result don't show all the information about the movie, how to change the SQL so that I can select all fields?

Answer 1

Basicly, I suppose you should use LEFT JOIN instead of INNER JOIN on such situation:

SELECT Films.Title, 
  Films.Date, 
  Films.Budget, 
  Persons.FirstName, 
  Persons.LastName, 
  Roles.RoleName, 
  Genres.Name 
FROM Films LEFT JOIN FilmPersons ON Films.FilmID = FilmPersons.FilmID 
INNER JOIN Persons ON FilmPersons.PersonID = Persons.PersonID 
INNER JOIN Roles ON FilmPersons.RoleID = Roles.RoleID 
LEFT JOIN FilmGenres ON Films.FilmID = FilmGenres.FilmID 
INNER JOIN Genres ON FilmGenres.GenreID = Genres.GenreID

While using LEFT JOIN,

FROM Films **LEFT JOIN** FilmPersons ON Films.FilmID = FilmPersons.FilmID

It would make sure that Films are the main collection, even some value of FilmPersons were missing. If you are using INNER JOIN , the final result of the query would be Intersection .

I'm not sure my explain is understandable..

Answer 2

Whats going to happen is for every row in films SQL Server will attempt to find matching rows in filepersons (if it does not find a matching row it will place nulls in the values that don't match) and so on. Where ever it finds a match it will put the values it finds in the matching columns otherwise it will place nulls in those columns.

SELECT Films.Title, 
  Films.Date, 
  Films.Budget, 
  Persons.FirstName, 
  Persons.LastName, 
  Roles.RoleName, 
  Genres.Name 
FROM Films LEFT JOIN FilmPersons ON Films.FilmID = FilmPersons.FilmID 
left JOIN Persons ON FilmPersons.PersonID = Persons.PersonID 
left JOIN Roles ON FilmPersons.RoleID = Roles.RoleID 
LEFT JOIN FilmGenres ON Films.FilmID = FilmGenres.FilmID 
left JOIN Genres ON FilmGenres.GenreID = Genres.GenreID