MySQL使用Where选择，如果不存在where条件则默认 [英] Mysql select with Where and default if where condition not present

问题描述

我有表格Product和productDetails.在productDetails中，我有用多种语言描述产品的行(由lang列区分).并非每种产品都有每种语言的描述.如何进行选择，以选择指定语言的描述(通过Where productDescription.lang = 'en')，如果不存在指定语言，则选择默认语言的描述(始终使用默认语言的描述).

I have tables Product and productDetails. In productDetails I have rows with description of product in many languages (discriminated by lang column). Not every product will have description in every language. How to make a selection that will select the description in the specified language (by Where productDescription.lang = 'en') and that will select a description in a default language if the specified language is not present (descriptions with default language are always present).

我做到了:

select *
  from product
  left join productDetails on product.id = productDetails.product_id
 where productDetails.language = 'en';

然后我用英语获得了所有详细信息.如果不存在en，如何修改此项以使用默认语言显示详细信息?

and I get all details in en language. How to modify this to make details in default language selected if en is not present?

推荐答案

类似的东西.我不知道您的确切架构:

Something like that. I don't know your exact schema:

select 
   p.id, 
   if(IS NULL d2.description, d1.description, d2.description ) `description`
 from product p
 join productDetails d1
   on product.id = productDetails.product_id
      and
   productDetails.language = 'default_lang'
 left join productDetails d2
   on product.id = productDetails.product_id 
      and
   productDetails.language = 'en'

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