SQL表与自身比较

Question

Movie(title, year, director, budget, earnings) 
Actor(stagename, realname, birthyear) 
ActedIn(stagename, title, year, pay) 
CanWorkWith(stagename, director) 

找到这样的演员 与stagename1在同一部电影与stagename2演员担任，但赚得少 的，作用艺名的所有对（改名stagename1和stagename2）电影。

SELECT A.stagename, B.stagename 
FROM ActedIn A 
LEFT JOIN ActedIn B ON A.title = B.title AND A.year = B.year 
      AND B.pay > A.pay 
WHERE B.name IS NOT NULL 

不能确定此处判定B.name IS NOT NULL是有效

Answer 1

SELECT A.stagename, B.stagename 
FROM ActedIn A 
INNER JOIN ActedIn B ON A.title = B.title 
AND A.year = B.year AND B.pay > A.pay 
WHERE B.name IS NOT NULL 

LEFT JOIN将是没有用的，如果你不想NULL值弗朗B.

Answer 2

http://sqlfiddle.com/#!2/67568/1

select a1.stagename as stagename1, a2.stagename as stagename2, a1.title 
from ActedIn as a1 
inner join ActedIn as a2 on (a1.title = a2.title and a1.year = a2.year) 
where a1.pay < a2.pay