mysql - 不同表之间的条件连接以组合不同的列

Question

我有三个表:

1. 产品分类
2. 分类单元
3. 标签

我想连接表以获得结果中的一列以满足:

• 如果tags.tag_name=“type”且tags.value=“Silver”，那么它应该包含两个条目 -taxons.name 和 concat(tags.value,taxon.name) 例如。

  products_taxons# 1,1
  分类群#1，“耳环”...
  标签# 1, 1, "类型", "银"

  结果列应包含“Earrings”和“SilverEarrings”

• 如果tags.tag_name=“type”且tags.value=“Precious”，那么它应该包含一个条目 - concat(tags.value,taxon.name)

  products_taxons# 2,1
  分类群#1，“耳环”...
  标签# 2, 2, "类型", "珍贵"

  结果列应包含“PreciousEarrings”

• 所有其他情况 - 带taxons.name的单一条目

我编写了以下 sql 查询。它有效，但有更好、最佳的方法吗？

select pt.product_id as product_id, concat(tag.value,t.name) as taxon
from taxons as t
inner join products_taxons as pt on t.id = pt.taxon_id
left join tags as tag
on tag.taggable_id = pt.product_id and (tag.value='Precious' or tag.value='Silver')
UNION ALL ( select pt.product_id as product_id, t.name as taxon
from taxons as t
inner join products_taxons as pt on t.id = pt.taxon_id
left join tags as tag
on tag.taggable_id = pt.product_id
where tag.value='Silver' )

编辑:例如，考虑下表条目

product_id | taxon_id  
------------+-----------
 1000000001 | 1
 1000000002 | 2
 1000000003 | 3


    id     |     name      
-----------+---------------
         1 | Necklace Sets
         2 | Earrings
         3 | Bracelets

product_id |       tag_name        |                   value                    
------------+-----------------------+--------------------------------------------
 1000000001 | type                  | Silver
 1000000002 | type                  | Precious
 1000000003 | occasion              | Everyday Wear

我想要以下结果

product_id | taxon  
------------+-----------
 1000000001 | Necklace Sets
 1000000001 | SilverNecklace Sets
 1000000002 | PreciousEarrings
 1000000003 | Bracelets

Answer 1

我认为这就是您正在寻找的:

select pt.product_id as product_id, 
case tag.value when "Silver" then concat(tag.value,t.name)
when "Precious" then concat(tag.value,t.name)
else t.name
 end as taxon

from taxons as t
inner join products_taxons as pt on t.id = pt.taxon_id
left join tags as tag
on tag.product_id = pt.product_id