Question

我有三个表：

1）本书

Column   Type                           | book_id | isbn | title | year |
book_id  integer Auto Increment PK      |    1    | 1234 | Book1 | 1999 |
isbn     character varying(30) UNIQUE   |    2    | 1235 | Book2 | 1999 |
title    character varying(150)         |    3    | 1236 | Book3 | 2009 |
year     smallint

2）作者

Column      Type                        | author_id |    name     |
author_id   integer Auto Increment  PK  |    5      |  Joe Doe    |
name        character varying(100)      |    7      |  John Curry |
                                        |    9      |  Jim Webb   |
                                        |   11      |  Carl Lee   |

3）book_author

Column     Type                                 | book_id | author_id |
book_id    integer REFERENCES book(book_id)     |    1    |     5     |
author_id  integer REFERENCES author(author_id) |    1    |     7     |
PRIMARY KEY (book_id, author_id)                |    2    |     9     |
                                                |    3    |    11     |

一本书可以有一个或多个作者，所以我决定创建book_author表以将书和author表连接在一起。我想创建一个查询来选择例如：1999年写过的所有书的书名和作者名。此查询应返回如下内容：

title name
Book1 Joe Doe
Book1 John Curry
Book2 Jim Webb

我设法创建了两个以某种方式实现此目的的查询（不是很完全）。

SELECT name from author WHERE author_id = 
ANY (SELECT author_id FROM book_author WHERE book_author.book_id = 1)

SELECT title FROM book WHERE book_id = ANY 
(SELECT book_id FROM book_author WHERE author_id = 5 OR author_id = 7)

您能为我提供一个可以达到上述目的的查询吗？如果您解释查询的结构及其背后的原因，那将是很好的。预先谢谢你

Answer 1

您可以读出Joins Between Tables

Select b.title, a.name from book_author ba 
    join author a on (a.author_id =ba.author_id) 
    join book b on (ba.book_id = b.book_id)
    where b.year=1999

查询结果：

title  name 
Book1  Joe Doe 
Book1  John Curry 
Book2 Jim Webb

Answer 2

加入表，您可以选择书名，然后由作者选择book_author，这是包含交易数据的源表，并与查找表（书和作者）结合以获取有关这些交易的信息。

 Select b.title,a.name from book_author as ba 
 inner join author as a on ba.author_id=a.author_id
 Inner join book as b on b.book_id=ba.book_id

PostgreSQL中的嵌套SELECT查询

2 个答案: