MYSQL IF语句到不同的WHERE子句

Question

I'm trying to solve a question on my app, i have this query to try to make it work.

SELECT * FROM articles
(IF articles.type = 1, INNER JOIN members ON members.id_member = articles.author_id,
INNER JOIN company ON company.id_company = articles.author_id) AS user
WHERE articles.tipe = '1' AND  user = '1';

I have a systems that post articles, but the same user can post on his name or in the name of a company that he has created, so, What i'm trying to do is, if the articles.tipe is type 1, then the article was published by his company, and if otherwise, it's type 0, then it's posted by him on his own name, if i only use 1 of them, they will get mixed, i've tryed different approches but none of them seem to work for me, can anybody help please?

Answer 1

You can left join both tables. For each articles record, one of the joined records will have values, the other will have all nulls. You can use coalesce on the columns or a case expression.

SELECT a.*, coalesce(m.name,c.name) as username
FROM articles a
LEFT JOIN members m ON m.id_member = a.author_id and a.type = '0'
LEFT JOIN company c ON c.id_company = a.author_id and a.type = '1'
WHERE a.user = '1';

Answer 2

you should use inner join to fetch only articles which have member id and company id for article type=1. so article_type condition will come in where condition and we will use inner join with member and company table.

Following query will give all the articles which have article type

select * from articles INNER JOIN members ON members.id_member = articles.author_id INNER JOIN company ON company.id_company = articles.author_id  where articles.type=1 and user=1

please add some more clarification if you think i am not understanding your question properly. Hope this helps you.

Answer 3

To get records for both article_type=0 and article_type=1 with conditional joins based on article type, here is the query:

select * from (

  select article.type,article.name,member.name as user from articles INNER JOIN members                         ON members.id_member = articles.author_id where article_type=0

 UNION ALL

 select article.type,article.name,company.name as user from articles INNER JOIN members       ON members.id_member = articles.author_id INNER JOIN company ON company.id_company = articles.author_id  where article_type=1

) as tmptbl;