MySQL-使用条件执行JOIN

Question

I have 2. tables: videos and videos_lang. I join these tables with LEFT JOIN when I want to get information about a video in selected language. And here is the problem: if the translation in selected language doesn't exist, I want to join translation in default language (which always exists). How can I do that? I use that sql query:

SELECT vl.\*, v.* 
FROM videos v 
LEFT JOIN videos_lang vl 
ON vl.sig = 'de' AND v.idVideo = vl.idVideo

How to get translation where vl.sig = 'en' (en is the defualt language)?

Answer 1

Try this query -

SELECT
  IFNULL(vl.idVideo, vl_en.idVideo),
  v.*
FROM videos v
LEFT JOIN (SELECT * FROM videos_lang WHERE sig = 'de') vl
  ON v.idVideo = vl.idVideo
LEFT JOIN (SELECT * FROM videos_lang WHERE sig = 'en') vl_en
  ON v.idVideo = vl_en.idVideo

Answer 2

You can try using OR condition inside your join query like this

SELECT vl.*, v.* FROM videos v LEFT JOIN videos_lang vl 
ON (vl.sig = 'de' OR vl.sig = 'en') AND v.idVideo = vl.idVideo