使用 Postgresql，当有桥 table 时，如何列出作者最早的书？

Question

我有三个 tables:

AUTHOR(auth_id, fname, lname)
BOOKAUTHOR(auth_id, book_id)
BOOK(book_id, book_name, publish_date)

AUTHOR
auth_id  fname   lname
----------------------------
1        Bob     Bobson
2        Sam     Samson
3        Bill    Billson
4        Sally   Sallson
5        Mary    Marson

BOOKAUTHOR
auth_id    book_id
------------------
1          11
1          12
2          13
2          14
3          15
3          16
4          17
4          18
5          19
5          20

BOOK
book_id   book_name     publish_date
-------------------------------------
11        Bob Book 1    2015-06-05
12        Bob Book 2    2020-07-06
13        Sam Book 1    2016-04-03
14        Sam Book 2    2020-09-27
15        Bill Book 1   2013-08-20
16        Bill Book 2   2015-01-16
17        Sall Book 1   2012-06-27
18        Sall Book 2   2018-03-10
19        Mary Book 1   2003-08-01
20        Mary Book 2   2020-06-05

其中 BOOKAUTHOR 是一座桥梁 table。
我想要 return 三列：author_name、name_of_their_first_book 和 date_it_was_published.
到目前为止我有：

SELECT fname || ' ' || lname AS author_name, MIN(publish_date) AS publish_date
FROM author a, book b, bookauthor ba
WHERE a.auth_id = ba.auth_id
AND b.book_id = ba.book_id
GROUP BY author_name;

其中 return 个：

author_name    publish_date
------------------------------
Bob Bobson     2015-06-05
Sam Samson     2016-04-03
Bill Billson   2013-08-20
Sally Sallson  2012-06-27
Mary Marson    2003-08-01

但是当我尝试添加书名时，如下所示

SELECT a.fname || ' ' || a.lname AS author_name, MIN(b.publish_date) AS publish_date, b.book_name AS latest_book
FROM author a, book b, bookauthor ba
WHERE a.auth_id = ba.auth_id
AND b.book_id = ba.book_id
GROUP BY author_name;

它return是作者所有书籍的列表，忽略了 MIN(b.publish_date):

author_name    publish_date   latest_book
-------------------------------------------
Bob Bobson     2015-06-05     Bob Book 1
Bob Bobson     2020-07-06     Bob Book 2
Sam Samson     2016-04-03     Sam Book 1
Sam Samson     2020-09-27     Sam Book 2
Bill Billson   2013-08-20     Bill Book 1
Bill Billson   2015-01-16     Bill Book 2
Sally Sallson  2012-06-27     Sall Book 1
Sally Sallson  2018-03-10     Sall Book 2
Mary Marson    2003-08-01     Mary Book 1
Mary Marson    2020-06-05     Mary Book 2

我认为正确的解决方案是以某种方式使用连接，但我还没有完全了解它们。如果是联结，您能否也解释一下他们在做什么？

Answer 1

您可以使用连接和 distinct on:

select distinct on (a.auth_id) a.*, b.*
from author a
inner join bookauthor ba on ba.auth_id = a.auth_id
inner join book b on b.book_id = ba.book_id
order by a.auth_id, b.publish_date

使用 Postgresql，当有桥 table 时，如何列出作者最早的书？

Working with Postgresql, how do I list an author's earliest book when there is a bridge table?

sql

postgresql

inner-join

greatest-n-per-group