【简答题】关系代数运算中,传统的集合运算有:并,交,差,____。关系代数运算中,专门的关系运算有选择、___________、连接和除等。关系代数的五种基本运算包括 ____________________ ___ 。[答案用顿号或者空格分隔]
【单选题】It really puzzles me that sometimes my parents encourage me _____ some friends and discourage me _____ with others. [ ]
B.
to stay with; from going
C.
staying with; from going
【简答题】It struck me that he might not have told the truth. →It _____________me that he might not have told the truth.
【单选题】It was ______ told them the news.
【单选题】It suddenly to me that this was something that I should never do, so I turned down her request.
【多选题】下列描述中,正确的有:()
A.
如何构造出一个合适的数据逻辑结构是关系数据库规范化理论主要解决的问题
B.
SQL语言提供数据库定义、数据操纵、数据控制等功能
C.
数据库保护问题包括: 安全性保护、完整性、故障恢复和并发控制等多方面
D.
关系代数中专门的关系运算包括: 选择、投影、连接和除法