Question

问题是

对于每位作者，请返回其第一本书的标题和出版日期。结果集应包含五列：作者的ID，作者的姓名，书的ID，书的标题和书的发布日期。

除了要显示每位作者的每本书以及必填项之外，我还有其他想要的输出列，如何获得只显示最早发布日期的书呢？

SELECT authors.id, authors.author, books.id, books.title, books.published_date

FROM authors

INNER JOIN books

ON authors.id = books.author_id

Answer 1

解决此问题的一种方法是使用一个查询，该查询为每个作者从表册中获取最小发布日期，然后将其联接到2个表中：

select 
  a.id, a.author,
  b.id, b.title, b.published_date
from authors a 
inner join books b on b.author_id = a.id
inner join (
  select author_id, min(published_date) published_date
  from books
  group by author_id
) g on g.author_id = b.author_id and g.published_date = b.published_date

Answer 2

如果使用最新版本的sqlite（3.25或更高版本），则可以使用window functions作为一种干净的方法：

给出此示例数据库：

CREATE TABLE authors(id INTEGER PRIMARY KEY, author TEXT);
INSERT INTO authors VALUES (1, 'John Steinbeck'), (2, 'William Faulkner');
CREATE TABLE books(id INTEGER PRIMARY KEY
                 , author_id INTEGER REFERENCES authors(id)
                 , title TEXT, published_date TEXT);
INSERT INTO books(author_id, title, published_date) VALUES
 (1, 'The Grapes Of Wrath', '1939-04-14'),
 (2, 'As I Lay Dying', '1930-10-06'),
 (2, 'The Sound And The Fury', '1929-10-07'),
 (1, 'East Of Eden', '1952-09-19'),
 (1, 'Tortilla Flat', '1935-01-01');

此查询：

WITH ranked(author_id, author, book_id, title, published_date, published_order) AS
 (SELECT a.id, a.author, b.id, b.title, b.published_date
       , rank() OVER (PARTITION BY a.id ORDER BY b.published_date)
  FROM authors AS a
  JOIN books AS b ON a.id = b.author_id)
SELECT author_id, author, book_id, title, published_date
FROM ranked
WHERE published_order = 1
ORDER BY author_id;

将产生：

author_id   author          book_id     title          published_date
----------  --------------  ----------  -------------  --------------
1           John Steinbeck  5           Tortilla Flat  1935-01-01    
2           William Faulkn  3           The Sound And  1929-10-07

对于每位作者，它会按出版顺序为每本书分配一个等级（在CTE中计算为rank() OVER (PARTITION BY a.id ORDER BY b.published_date)列），然后仅选择排名为1的图书作为最终结果。

如何归还每位作者出版的第一本书？

2 个答案: