资质 |门 CS 1998 |第 62 题

假设我们有一个由以下三个关系组成的数据库。

FREQUENTS(student, parlor) giving the parlors each student visits.
SERVES(parlor, ice-cream) indicating what kind of ice-creams each parlor serves.
LIKES(student, ice-cream) indicating what ice-creams each parlor serves.

(Assuming that each student likes at least one ice-cream and frequents at least one parlor)

用 SQL 表达以下内容：
打印至少光顾一间供应他们喜欢的冰淇淋的客厅的学生。回答：
解释：答案：

SELECT DISTINCT FREQUENTS.student FROM  
   FREQUENTS, SERVES, LIKES
   WHERE
       FREQUENTS.parlor=SERVES.parlor  
       AND
       SERVES.ice-cream=LIKES.ice-cream
       AND
       FREQUENTS.student=LIKES.student; 

这个问题的测验