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()。
实体完整性规则是对()的约束,参照完整性规则是对()的约束。
关系中不允许有重复元组的原因是()
Today there are ()computers in our homes and offices than there are people who live and work in them. less。 more。 little。 lotsof。
Very long, complex expressions in program are difficult to write correctly and difficult to(). defend。 detect。 default。 debug。
00P was invented because procedural languages, such as(),Pascal, and BASIC.