Question

我有三个表，Book（Bookid，title）和Movie（Movieid，title）和checkout（memberid，bookid，movieid）。

Movie:

id          title
----------  -------------
1           Life of Brian
2           Airplane
3           Rush
4           Day of the De
5           Star Wars
6           Thin Red Line
7           Crouching Tig
8           Lawrence of A
9           Office Space

Book:

id          title
----------  ----------
1           Life of Pi
2           Fellowship
3           Two Towers
4           Dune
5           The Hobbit
6           1984
7           Tom Sawyer
8           Catcher in
9           To Kill a
10          Domain Dri

Checkout:

member_id   book_id     movie_id
----------  ----------  ----------
6           1
1           3
2           4
1           5
1                       1
7                       2
6                       3
8                       4
6                       5

我想选择所有尚未签出的书籍和电影。

目前我正在使用这些查询。

create table MoviesNotCheckedOut (MovieID integer, MovieName text);

    Insert Into MoviesNotCheckedOut 
    select m.id, m.title from movie m where 
    m.id NOT IN  
    (select c.member_id from checkout_item c);

    create table BooksNotCheckedOut (BookID integer, BookName text);

    Insert Into BooksNotCheckedOut 
    select b.id, b.title from book b where 
    b.id NOT IN  
    (select c.member_id from checkout_item c);

create table BooksAndMoviesNotCheckedOut(BookID integer, BookName text, MovieID integer, MovieName text);

insert into BooksAndMoviesNotCheckedOut
select b.BookID,b.BookName,m.MovieID,m.MovieName from BooksNotCheckedOut b, MoviesNotCheckedOut m;

但在显示时我得到的重复是这样的：

BookID      BookName    MovieID     MovieName
----------  ----------  ----------  ----------
3           Two Towers  3           Rush
3           Two Towers  4           Day of the
3           Two Towers  5           Star Wars
3           Two Towers  9           Office Spa
4           Dune        3           Rush
4           Dune        4           Day of the
4           Dune        5           Star Wars
4           Dune        9           Office Spa
5           The Hobbit  3           Rush
5           The Hobbit  4           Day of the
5           The Hobbit  5           Star Wars
5           The Hobbit  9           Office Spa
9           To Kill a   3           Rush
9           To Kill a   4           Day of the
9           To Kill a   5           Star Wars
9           To Kill a   9           Office Spa
10          Domain Dri  3           Rush
10          Domain Dri  4           Day of the
10          Domain Dri  5           Star Wars
10          Domain Dri  9           Office Spa

如何删除重复项。我希望将其显示为：

BookID     BookName     MovieID     MovieName
_ _ _      _ _ _ _      _ _ _ _     _ _ _ _ _ _

1           xxxx          4          yyyy

Answer 1

您可以使用union all;但是，您应该将其作为两列：

select 'movie' as which, m.id, m.title
from movie m
where not exists (select 1 from checkout co where co.movieid = m.id)
union all
select 'book' as which, b.id, b.title
from book b 
where not exists (select 1 from checkout co where co.bookid = b.id);

合并两个不相关的表

1 个答案: