rel-ops.txt

来自「开耐饥梅陇大学 网上教程 ssd7 exercise1 和exercise4答案」· 文本 代码 · 共 10 行

In order to perform the this query, I have used Project, Select
and Join operations.

Project: Select the attributes specified on an attribute_list from
         the table BOOK, that is "Title" and "Price".
Select: Selects some rows in the table BOOK that satisfy a selection 
        condition (alias predicate). That is "WHERE (BOOK.PubID=PUBLISHER.PubID) AND(PUBLISHER.Name='DannyShum' or PUBLISHER.Name='LionLi')".
Join:  The Join operation combines two tables, thereby allowing us to obtain more information.
       To be combined, the rows from each table must satisfy a joining condition. 
       That is "WHERE (BOOK.PubID=PUBLISHER.PubID) AND(PUBLISHER.Name='DannyShum' or PUBLISHER.Name='LionLi')".