Question

我有三张桌子：

products_taxons
taxons
标签

我想加入表格以获得结果中的列以满足：

如果tags.tag_name =＆＃34;输入＆＃34;和tags.value =＆＃34; Silver＆＃34;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＃1，＆＃34;耳环＆＃34; ...
标签＃1,1，＆＃34;类型＆＃34;，＆＃34;银＆＃34;

结果列应包含＆＃34;耳环＆＃34;和＆＃34; SilverEarrings＆＃34;
如果tags.tag_name =＆＃34;输入＆＃34;和tags.value =＆＃34; Precious＆＃34;那么它应该包含一个条目 - concat（tags.value，taxon.name）

products_taxons＃2,1
分类＃1，＆＃34;耳环＆＃34; ...
标签＃2,2，＆＃34;输入＆＃34;，＆＃34; Precious＆＃34;

结果列应包含＆＃34; PreciousEarrings＆＃34;
1. 所有其他情况 - 使用taxons.name

我编写了以下sql查询。它有效，但是有更好的，最佳的方式吗？

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：示例，请考虑以下表格条目

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

我认为这就是你要找的东西：

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

不同表之间的条件连接以组合不同的列

1 个答案: