精选优质文档-倾情为你奉上1. A primary key is a field (or group of fields) that uniquely describes each record in the database. T2. Data redundancy improves the integrity of a database. 3. SQL is the language used by relational databases to create objects and to manipulate and retrieve data.4. A relational database management system does not include tools for backing up & restoring databases. 5. 1，一种主键是一个字段（或字段组）唯一地描述了每个记录在数据库中。6. 2.数据冗余改善了数据库的完整性。7. 3，SQL是关系型数据库用于创建对象，并以操作和检索数据的语言。8. 4
