如何使用交叉联接查找行>列组合?[SQL] [英] How to find rows>columns combinations with Cross Join? [SQL]
本文介绍了如何使用交叉联接查找行>列组合?[SQL]的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
我想创建来自不同类别ID的项目组合.
I want to create a combination of items from different categories ids.
你能帮我吗?
表
+---------+-------------+------------+
| post_id | category_id | post_title |
+---------+-------------+------------+
| 1 | 1 | Red |
| 2 | 1 | Black |
| 3 | 2 | Medium |
| 4 | 3 | Male |
| 5 | 3 | Female |
+---------+-------------+------------+
我想要的查询结果如下:
Red-Medium-Male
Black-Medium-Male
Red-Medium-Female
Black-Medium-Female
例如,如果有属于6个不同类别的项目,则如下所示:
For example, if there were items belonging to 6 different categories, it would be like below:
Red-Medium-Male-Other1-Other2-Other3
推荐答案
您可以使用交叉连接
和过滤:
select t1.post_title, t2.post_title, t3.post_title
from t t1 cross join
t t2 cross join
t t3
where t1.category_id = 1 and
t2.category_id = 2 and
t3.category_id = 3;
您可以使用递归CTE对此进行概括:
You can generalize this using a recursive CTE:
with recursive tt as (
select t.*, dense_rank() over (order by category_id) as cat_seqnum
from t
),
cte as (
select cat_seqnum, post_title
from tt
where cat_seqnum = 1
union all
select tt.cat_seqnum, concat_ws('-', cte.post_title, tt.post_title)
from cte join
tt
on tt.cat_seqnum = cte.cat_seqnum + 1
)
select *
from cte
where cat_seqnum = (select max(cat_seqnum) from tt);
此处是db小提琴.
这篇关于如何使用交叉联接查找行>列组合?[SQL]的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!
查看全文