我是 SQL 的新手，需要帮助我有 4 个表:

helmet                                  arm
+------+---------+-----+--------+       +------+---------+-----+--------+
|  id  |   name  | def | weight |       |  id  |   name  | def | weight |
+------+---------+-----+--------+       +------+---------+-----+--------+
|   1  |  head1  |  5  |   2.2  |       |   1  |   arm1  |  4  |   2.7  |
|   2  |  head2  |  6  |   2.9  |       |   2  |   arm2  |  5  |   3.1  |
|   3  |  head3  |  7  |   3.5  |       |   3  |   arm3  |  2  |   1.8  |
+------+---------+-----+--------+       +------+---------+-----+--------+

body                                    leg
+------+---------+-----+--------+       +------+---------+-----+--------+
|  id  |   name  | def | weight |       |  id  |   name  | def | weight |
+------+---------+-----+--------+       +------+---------+-----+--------+
|   1  |  body1  |  10  |  5.5  |       |   1  |   leg1  |  8  |   3.5  |
|   2  |  body2  |  5   |  2.4  |       |   2  |   leg2  |  5  |   2.0  |
|   3  |  body3  |  17  |  6.9  |       |   3  |   leg3  |  8  |   1.8  |
+------+---------+-----+--------+       +------+---------+-----+--------+`

我正在寻找最高的 totaldef which totalweight <=>
像这样:总重量 <=>

查询:

select 
    helmet.name as hname, body.name as bname, 
    arm.name as aname, leg.name as lname,
    helmet.poise + body.poise + arm.poise + leg.poise as totalpoise, 
    helmet.weight + body.weight + arm.weight + leg.weight as totalweight 
from 
    helmet 
inner join 
    body on 1=1
inner join 
    arm on 1=1
inner join 
    leg on 1=1 
where 
    helmet.weight + body.weight + arm.weight + leg.weight <= 10
order by 
    totalpoise desc 
limit 5

结果:

+-------+-------+-------+-------+----------+-------------+
| hname | bname | aname | lname | totaldef | totalweight |
+-------+-------+------ +-------+----------+-------------+
| head2 | body2 |  arm1 |  leg3 |    23    |     9.8     |
| head1 | body2 |  arm2 |  leg3 |    23    |     9.5     |
| head3 | body2 |  arm3 |  leg3 |    22    |     9.5     |
| head1 | body2 |  arm1 |  leg3 |    22    |     9.1     |
| head2 | body2 |  arm3 |  leg3 |    21    |     8.9     |
+-------+-------+-------+-------+----------+-------------+

问题是每个表大约有 100 行，因此可能的结果是 1 亿多行。查询需要很长时间。我不确定这与我的硬件或数据库或查询类型有关。

P.S:我使用 HDD 并有 8GB 内存。我已经在 MySQL 和 PostgreSQL 上进行了测试。

更新 我还没有创建索引。

这是解释计划吗？ explain plan

需要多长时间？ 这取决于输入。 在 MySQL 上大约需要几分钟 - 几个小时。
在 PostgreSQL 上大约需要 30 秒 - 2 分钟。

更新 2 我的表格永远不会改变。那么我可以将所有结果存储在一个表中吗？有帮助吗？

更新 3 我考虑分区。它可能快得多，但问题是如果下分区中的某些 [armor set] 的 totaldef 比上分区中的 [armor set] 多。 示例:

[head1,arm1,body1,leg1][totaldef 25][totalweight 9.9]
[head2,arm2,body2,leg2][totaldef 20][totalweight 11.0]

所以分区总重量 >10 会错过那个 [armor set]，因为它在其他分区中。

这是供任何想要测试的人使用的 CSV 文件。 CSV file

更新 4 我认为最快的方法是创建 materialized view但我想性能的关键是对其进行排序。我不知道哪种排序可以帮助物化 View 或索引，但我对它们都进行了排序并且很有用。

没想到会得到这么多帮助。谢谢。

最佳答案

A materialized view具有适当索引的性能相当不错，在我使用 Postgresql 配置的老化 SSD 桌面上运行 1.8 秒:

create materialized view v as
select
    h.name as hname, b.name as bname, a.name as aname, l.name as lname,
    total_poise, total_weight
from
    helmet h
    cross join
    body b
    cross join
    arm a
    cross join
    leg l
    cross join lateral (
        select
            h.weight + b.weight + l.weight + a.weight as total_weight,
            h.poise + b.poise + l.poise + a.poise as total_poise
    ) total
order by total_poise desc, total_weight
;

create index v_index on v (total_poise desc, total_weight);

执行与分析:

select *
from v
where total_weight <= 10
order by total_poise desc, total_weight
limit 5
;
         hname         |          bname           |         aname          |          lname           | total_poise | total_weight 
-----------------------+--------------------------+------------------------+--------------------------+-------------+--------------
 Fume Sorcerer Mask+10 | Moon Butterfly Wings+5   | Velstadt`s Gauntlets+5 | Prisoner`s Waistcloth+10 |          20 |          9.4
 Fume Sorcerer Mask+10 | Lion Warrior Cape+10     | Velstadt`s Gauntlets+5 | Prisoner`s Waistcloth+10 |          20 |          9.5
 Fume Sorcerer Mask+10 | Red Lion Warrior Cape+10 | Velstadt`s Gauntlets+5 | Prisoner`s Waistcloth+10 |          20 |          9.5
 Fume Sorcerer Mask+10 | Moon Butterfly Wings+5   | Velstadt`s Gauntlets+5 | Lion Warrior Skirt+10    |          20 |          9.6
 Fume Sorcerer Mask+10 | Moon Butterfly Wings+5   | Velstadt`s Gauntlets+5 | Moon Butterfly Skirt+10  |          20 |          9.6


explain analyze
select *
from v
where total_weight <= 10
order by total_poise desc, total_weight
limit 5
;
                                                             QUERY PLAN                                                              
-------------------------------------------------------------------------------------------------------------------------------------
 Limit  (cost=0.57..11.71 rows=5 width=88) (actual time=1847.680..1847.694 rows=5 loops=1)
   ->  Index Scan using v_index on v  (cost=0.57..11191615.70 rows=5020071 width=88) (actual time=1847.678..1847.691 rows=5 loops=1)
         Index Cond: (total_weight <= '10'::double precision)
 Planning time: 0.126 ms
 Execution time: 1847.722 ms

关于mysql - 是否有可能更快地获得查询？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/42312741/