性能休眠 @Subselect 与数据库视图

Question

我有一个Java8 Spring基于Boot 2.3.3的应用程序（使用hibernate 5.4.20），我有一个Postgresql。我想最终了解使用或不使用数据库视图和/或 @Subselect.

是否更好（为了性能）

快速概览：我有一个实体“Book”和 3 个实体“BookRank”（用户给书 1 到 10 星），“BookComment”（用户comments to the book) , "BookLike" (users put like to the books) 每个都有 Book 关系 (ManyToOne)，所以在我的查询结果中，我想以这种方式订购书籍:

order by avg(book_rank) desc, sum(book_rank) desc, count(book_comment) desc, count(book_like) desc

当然有很多书，很多排名，评论和喜欢...:)

我找到了 4 种方法来做同样的事情，从内部有 3 个子 select 的复杂查询开始（这对我来说是最好的解决方案，但如果有人有更好的方法做请告诉我）。

select *
from(
    select bbb.id as book_id, min(bbb.b_rank_average) as b_rank_average, min(bbb.b_rank_sum) as b_rank_sum, min(bbb.b_comment_count) as b_comment_count, count(b_l.id) as b_like_count
    from(
        select rr.id, min(bb.b_rank_average) as b_rank_average, min(bb.b_rank_sum) as b_rank_sum, count(b_c.id) as b_comment_count
        from(           
            select b.id,  avg(b_r.rank) as b_rank_average, sum(b_r.rank) as b_rank_sum
            from book as b
            left join book_rank as b_r on (b.id = b_r.book_id and b_r.deleted = false)
            group by b.id) as bb
            
        left join book_comment as b_c on (bb.id = b_c.book_id and b_c.deleted = false)
        group by bb.id) as bbb
                
    left join book_like as b_l on (bbb.id = b_l.book_id and b_l.deleted = false)
    group by bbb.id
    ) as bbbb
    
left join book on bbbb.book_id = book.id
where book.deleted = false
order by b_rank_average desc nulls last, b_rank_sum desc nulls last, b_comment_count desc, b_like_count desc, book_id desc;

我想知道哪一个性能最好...

1) 存储库中的纯本机查询 - 无视图 - 无不可变实体

在我的存储库中，我只有一个使用上面编写的本机查询的方法

2) 在存储库中使用数据库视图和本机查询

正在使用查询的中心部分创建数据库视图：

create or replace view book_ranking as

    select bbb.id as book_id, min(bbb.b_rank_average) as b_rank_average, min(bbb.b_rank_sum) as b_rank_sum, min(bbb.b_comment_count) as b_comment_count, count(b_l.id) as b_like_count
    from(
        select rr.id, min(bb.b_rank_average) as b_rank_average, min(bb.b_rank_sum) as b_rank_sum, count(b_c.id) as b_comment_count
        from(           
            select b.id,  avg(b_r.rank) as b_rank_average, sum(b_r.rank) as b_rank_sum
            from book as b
            left join book_rank as b_r on (b.id = b_r.book_id and b_r.deleted = false)
            group by b.id) as bb
            
        left join book_comment as b_c on (bb.id = b_c.book_id and b_c.deleted = false)
        group by bb.id) as bbb
                
    left join book_like as b_l on (bbb.id = b_l.book_id and b_l.deleted = false)
    group by bbb.id

并在存储库方法中修改本机查询以使用视图：

select * 
from book_ranking as the_view
left join book on the_view.book_id = book.id 
where book.deleted = false
order by b_rank_average desc nulls last, b_rank_sum desc nulls last, b_comment_count desc, b_like_count desc, book_id desc;

3) 具有数据库视图和不可变实体，select 存储库中的视图和 jpql 查询

使用实体（不可变）封装上面的视图

@Entity
@Subselect("select * from book_ranking")
public class BookRanking implements Serializable {
    ....
}

并修改加入 Book 实体和新 BookRanking 不可变实体（即视图）的存储库查询（非本机查询）

@Query("select b from BookRanking as b_r 
        join Book b on b_r.bookId = b.id 
        where b.deleted = false
        order by b_r.b_rank_average desc nulls last, b_r.b_rank_sum desc nulls last, b_r.b_comment_count desc, b_r.b_like_count desc, b_r.bookId desc)

4) @subselect 中的查询和存储库中的 jpql 查询没有视图但不可变实体

没有数据库视图，但不可变实体 BookRanking 在 @Subselect 注释中有查询，带有 'view query' 和 @Synchronize 注释，如下所示：

@Entity
@Subselect("select bbb.id as book_id, min(bbb.b_rank_average) as b_rank_average, min(bbb.b_rank_sum) as b_rank_sum, min(bbb.b_comment_count) as b_comment_count, count(b_l.id) as b_like_count
    from(
        select rr.id, min(bb.b_rank_average) as b_rank_average, min(bb.b_rank_sum) as b_rank_sum, count(b_c.id) as b_comment_count
        from(           
            select b.id,  avg(b_r.rank) as b_rank_average, sum(b_r.rank) as b_rank_sum
            from book as b
            left join book_rank as b_r on (b.id = b_r.book_id and b_r.deleted = false)
            group by b.id) as bb
            
        left join book_comment as b_c on (bb.id = b_c.book_id and b_c.deleted = false)
        group by bb.id) as bbb
                
    left join book_like as b_l on (bbb.id = b_l.book_id and b_l.deleted = false)
    group by bbb.id )

@Synchronize({ "book", "book_rank", "book_comment", "book_like" })

public class BookRanking implements Serializable {
    ....
}

并使用连接 Book 实体和第 3 点的新 BookRanking 不可变实体（类似于视图）的相同存储库查询（非本机查询）

Answer 1

一般来说，数据库视图只是一个扩展为查询计划的关系，通常是在解析期间，因此使用视图与直接写出整个查询应该没有显着差异。使用视图可以让您更轻松地重用查询，但是当您想要更改某些内容时，您将不得不更改视图，也许还必须更改使用该视图的所有应用程序，因此可重用性方面可能会让您反感。

我通常不推荐视图，因为我看到有人为了“让其他人更容易”而在视图中加入很多不必要的连接。未使用的连接的问题是，数据库通常无法消除它们。 TLDR，我建议直接在代码中写出查询，因为您可以省略不需要的连接，从而获得更好的性能。

您可以使用以下更简单的查询：

select 
    b.id, 
    avg(b_r.rank) as b_rank_average, 
    sum(b_r.rank) as b_rank_sum,
    (select count(*) from book_comment as b_c where b.id = b_c.book_id and b_c.deleted = false) as b_comment_count
    (select count(*) from book_like as b_l where b.id = b_l.book_id and b_l.deleted = false) as b_like_count
from book as b
left join book_rank as b_r      on (b.id = b_r.book_id and b_r.deleted = false)
where b.deleted = false
group by b.id
order by b_rank_average desc nulls last, b_rank_sum desc nulls last, b_comment_count desc, b_like_count desc, b.id desc

也可以用 JPQL/HQL 查询建模。它看起来非常相似：

select 
    b.id, 
    avg(r.rank) as b_rank_average, 
    sum(r.rank) as b_rank_sum,
    (select count(*) from b.comments c where c.deleted = false) as b_comment_count
    (select count(*) from b.booksLike l where l.deleted = false) as b_like_count
from book as b
left join b.ranks as r on r.deleted = false
where b.deleted = false
group by b.id
order by b_rank_average desc nulls last, b_rank_sum desc nulls last, b_comment_count desc, b_like_count desc, b.id desc

性能休眠 @Subselect 与数据库视图

Performance hibernate @Subselect vs database view

database

performance

hibernate

view

spring-boot