sql 一行join 如何多表条件关联?

SELECT a.name, b.sort 
FROM a
left join c on a.uid = c.id
LEFT JOIN b ON a.perid = b.id 
OR (a.perid IS NULL AND  a.bid  is not null and a.bid = b.id)
 or   (a.perid IS NULL AND  a.bid  is  null and  c.did  = b.id)