Sql 嵌套json_agg

我有一个postgresql查询，它返回一个json，其中包含所有书籍的标题、作者的名字和姓氏，以及一个包含所有书评标题+书评人的名字和姓氏的数组

SELECT json_build_object(
    'title', a.title,
    'author_firstname', b.firstname,
    'author_lastname', b.lastname,
    'reviews', json_agg(json_build_object(
        'review_title', c.title,
        'reviewer_firstname', d.firstname,
        'reviewer_lastname', d.lastname
    ))
)
FROM book AS a
INNER JOIN person AS b ON a.author_id = b.id
    LEFT JOIN review AS c ON c.book_id = a.id
    INNER JOIN person AS d ON c.reviewer_id = d.id
GROUP BY a.id, b.id

这很有效，而且速度很快。我需要扩展这个查询，以包括所有书名的书评人也

我遵循了第一个左连接使用的逻辑

SELECT json_build_object(
    'title', a.title,
    'author_firstname', b.firstname,
    'author_lastname', b.lastname,
    'reviews', json_agg(json_build_object(
        'review_title', c.title,
        'reviewer_firstname', d.firstname,
        'reviewer_lastname', d.lastname,
        'reviewer_books', json_agg(json_build_object(
            'book_title', e.title
        ))
    ))
)
FROM book AS a
INNER JOIN person AS b ON a.author_id = b.id
    LEFT JOIN review AS c ON c.book_id = a.id
    INNER JOIN person AS d ON c.reviewer_id = d.id
        LEFT JOIN book AS e ON e.author_id = d.id
GROUP BY a.id, b.id

但这不起作用，因为聚合函数调用不能嵌套。是否有一个解决方案，可以扩展到包括更深层的关系（如所有书评人的所有书评），并且相对有效

---

那些数据库把我弄糊涂了，谢谢你的帮助

您需要多个级别的聚合。这有点像：

SELECT json_build_object(
    'title', b.title,
    'author_firstname', p.firstname,
    'author_lastname', p.lastname,
    r.reviews
)
FROM book b INNER JOIN
     person p
     ON b.author_id = pb.id LEFT JOIN
     (SELECT r.book_id,
             json_agg(json_build_object('review_title', r.title,
                                        'reviewer_firstname', pr.firstname,
                                        'reviewer_lastname', pr.lastname,
                                        'reviewer_books', rb.reviewer_books
                                       )
                     ) as reviews
      FROM review r JOIN
           person pr
           on r.reviewer_id = pr.id JOIN
           (SELECT r2.reviewer_id, json_agg(json_build_object('book_title', b2.title) as reviewer_books
            FROM reviews r2 JOIN
                 book b2
                 ON r2.book_id = b2.id
            GROUP BY r2.reviewer_id
           ) rb
           on r.reviewer_id = rb.reviewer_id
    ) r
    on r.book_id = b.id;

---

您需要多个级别的聚合。这有点像：

SELECT json_build_object(
    'title', b.title,
    'author_firstname', p.firstname,
    'author_lastname', p.lastname,
    r.reviews
)
FROM book b INNER JOIN
     person p
     ON b.author_id = pb.id LEFT JOIN
     (SELECT r.book_id,
             json_agg(json_build_object('review_title', r.title,
                                        'reviewer_firstname', pr.firstname,
                                        'reviewer_lastname', pr.lastname,
                                        'reviewer_books', rb.reviewer_books
                                       )
                     ) as reviews
      FROM review r JOIN
           person pr
           on r.reviewer_id = pr.id JOIN
           (SELECT r2.reviewer_id, json_agg(json_build_object('book_title', b2.title) as reviewer_books
            FROM reviews r2 JOIN
                 book b2
                 ON r2.book_id = b2.id
            GROUP BY r2.reviewer_id
           ) rb
           on r.reviewer_id = rb.reviewer_id
    ) r
    on r.book_id = b.id;

---

使用任意字母作为表别名是一种非常糟糕的做法。您应该为表名使用缩写，例如

b

表示

book

和

p

表示

person

。使用任意字母作为表别名是非常糟糕的做法。表名应使用缩写，例如

b

表示

book

和

p

表示

person

。非常感谢！多谢各位！