查询1:这两个SQL查询有什么区别?
SELECT Frequents.drinker FROM Frequents
WHERE Frequents.drinker NOT IN (
SELECT F.drinker FROM Frequents AS F
WHERE F.bar NOT IN
(
SELECT bar FROM Sells, Likes WHERE Sells.beer = Likes.beer AND Likes.drinker = F.drinker
)
)
QUERY 2:
SELECT Frequents.drinker FROM Frequents, Sells, Likes
Where Frequents.drinker = Likes.drinker and Sells.bar IN(
SELECT bar from Sells where Sells.beer = Likes.beer)
关系模式
注:忽略拼写错误。
其中上述查询的是正确的“打印饮水服务于一些啤酒,他们喜欢 经常只吧。(假设每个 饮酒喜欢至少一个啤酒流连至少一个吧。)”
Q1是分配的解决方案,Q2是我提交的内容,我相信我的查询版本是正确的。 –