安全运算是指不产生()和()的运算。
关系代数的5个基本操作是()()()()()。
关系代数的理论基础是(),关系演算的理论基础是(),关系逻辑的理论基础是()。
00P was invented because procedural languages, such as(),Pascal, and BASIC. ["
A.C","C++","C#","asp"]
Most Computer operating systems in use today, including all consumer-targeted systems, include a TCP/IP(). ["plan","requirement","implementation","design"]
关系中不允许有重复元组的原因是()