题目内容

单选题 If a relation has five rows, then its () is five.

A. difference
B. cardinality
C. duplicity
D. relativity

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单选题（）is a declarative language used on relational databases.

A. PDQ
B. SQL
C. LES
D. PBJ

填空题 A DBMS users can be or programs.

填空题 In the history of database design, three models have been in use: the model, the model, themodel.

填空题 Each column in a relation is called an____.