如何使用Postgres联接表中只有一行？
我有以下结构：CREATE TABLE authorid integer,name varchar(255));CREATE TABLE bookid integer,author_id integer,title varchar(255),rating integer);我希望每个作者都能读到最后一本书：
SELECT book.id,author.id,author.name,book.title as last_bookFROM authorJOIN book book ON book.author_id = author.idGROUP BY author.idORDER BY book.id ASC显然，你可以在那里mysql执行此操作：在MySQL连接两个表，只从第二个表返回一行。
但是postgres给出这个错误：
错误：“ book.id必须出现列GROUP BY用于子句或聚合函数：SELECT
book.id，author.id，author.name，book.title为last_book FROM author JOIN book
book on book.author_id = author.id GROUP BY author.id ORDER BY book.id ASC
这是因为：
如果存在GROUP BY，则SELECT未分组列(聚合函数除外)不能引用列表表达式，因为未分组列将返回多个可能值。
我如何指定postgres：“仅joined_table.id在连接表中按顺序给我最后一行？
编辑：使用此数据：
INSERT INTO author (id,name) VALUES(1,'Bob(二)，David(3)，John');INSERT INTO book (id,author_id,title,rating) VALUES 1、1、1、1st book from bob五、nd book from bob六、rd book from bob七、st book from David(、nd book from David',6);我应该看到：
book_id author_id name last_book3 3 1 "Bob" "3rd book from bob"5 2 "David" "2nd book from David"
解决方案:
select distinct on (author.id) book.id,author.id,author.name,book.title as last_bookfrom author inner join book on book.author_id = author.idorder by author.id,book.id desc查看 distinct on
SELECT DISTINCT ON（expression [，…]）每组行的第一行只保留给定表达式。ORDER
BY解释相同的规则DISTINCT ON表达式(请参见上面)。请注意，除非使用。ORDER
BY确保所需的行先出现，否则每一集的第一行都是不可预测的。
内容独特，有必要在其中添加独特列order by。如果不是你想要的顺序，你需要包装查询并重新排序
select *fromselect distinct on (author.id) book.id,author.id,author.name,book.title as last_book from author inner join book on book.author_id = author.id order by author.id,book.id desc) authors_with_first_bookorder by authors_with_first_book.name另一种解决方案是使用Lennart答案中的窗口函数。另一个很常见的是
select book.id,author.id,author.name,book.title as last_bookfrom book inner join ( select author.id as author_id,max(book.id) as book_id from author inner join book on author.id = book.author_id group by author.id ) s on s.book_id = book.id inner join author on book.author_id = author.id
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