题目内容

单选题 Each column in a relation is called ().

A. an attribute
B. a tuple
C. a union
D. an attitude

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单选题 The degree of a relation is the number of () in the relation.

A. attributes
B. tuples
C. unions
D. attitudes

单选题 Each row in a relation is called ().

A. an attribute
B. a tuple
C. a union
D. an attitude

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

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

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

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