part3.txt

SSD7（数据库系统原理）Exercise 1

1. The result of the difference operation s-r is a table whose tuples      are menbers of s but not of r. It is like the belowing table:
    D     E     F
    b     g     a

2. If the query is retrieved by replacing UNION with EXCEPT, the result    will be a list of member numbers of all members currently borrowing     the book that has the call number QA76.9.D26C66 but not the call    number QA76.9.D7E53.