Question

所以我有一个问题，我试图解决几个星期，但我没有找到任何解决方案。所以这是我正在尝试查询的表： Tables

我显然加入了他们（简单）：

SELECT a.date,b.title,b.author,u.nick
FROM book_add a 
INNER JOIN user u on(a.user_fk=u.id) 
INNER JOIN book b on (a.book_fk=b.id) 
INNER JOIN status s ON(a.status_fk=s.id) 
WHERE s.description='active';

现在出现了问题：我想按日期desc排序并区分它们，以便最后一行插入的行（最新日期）是第一行。但是一旦他们得到区分，结果就很奇怪了。我试过这个：

SELECT a.date,b.title,b.author,u.nick
FROM book_add a 
INNER JOIN user u on(a.user_fk=u.id) 
INNER JOIN book b on (a.book_fk=b.id) 
INNER JOIN status s ON(a.status_fk=s.id) 
WHERE s.description='active' ORDER BY a.date DESC;

这是有效的，虽然一旦我尝试了distinctig a.book_fk结果是错误的：

SELECT DISTINCT ON(a.book_fk)a.book_fk,a.date,b.title,b.author,u.nick
FROM book_add a 
INNER JOIN user u on(a.user_fk=u.id) 
INNER JOIN book b on (a.book_fk=b.id) 
INNER JOIN status s ON(a.status_fk=s.id) 
WHERE s.description='active' ORDER BY a.date DESC;

我甚至尝试过像这样的方法，但没有成功：

SELECT * FROM (SELECT DISTINCT  
ON(a.book_fk)a.book_fk,a.date,b.title,b.author,u.nick
FROM book_add a
INNER JOIN user u on(a.user_fk=u.id) 
INNER JOIN book b on (a.book_fk=b.id) 
INNER JOIN status s ON(a.status_fk=s.id) 
WHERE s.description='active') res ORDER BY res.date DESC

有人可以帮助我吗？我会很开心的！谢谢！

Answer 1

听起来你正试图在每本书中获得一行，具有最新的用户/状态？在这种情况下，这应该有效：

SELECT DISTINCT ON(a.book_fk)
       a.book_fk, a.date, b.title, b.author, u.nick
FROM   book_add a 
INNER JOIN user u on(a.user_fk=u.id) 
INNER JOIN book b on (a.book_fk=b.id) 
INNER JOIN status s ON(a.status_fk=s.id) 
WHERE  s.description='active'
ORDER BY a.book_fk, a.date DESC
;

Postgresql查询问题

1 个答案: