【单选题】Which of the following is not a basic requirement of a relational database?
A.
Every column in a row must be single valued.
B.
Primary keys cannot be null.
C.
Foreign keys, if not null, must have values that correspond to the value of another foreign key in another table.
D.
All nonkey attributes in a table should describe a characteristic about the object identified by the primary key.
E.
All of the above are basic requirements of a relational database.
【简答题】人们根据特定的需要预先为计算机编制的指令序列称为().A. 软件 B. 文件 C. 程序 D. 集合
【单选题】人们根据特定的需要预先为计算机编制的指令序列称为()
【简答题】根据给出的短语,写出中文意思:relational database
【简答题】人们根据特定的需要预先为计算机编制的指令序列称为()
【单选题】人们根据特定的需要预先为计算机编制的指令序列称为().
【单选题】人们根据特定的需要预先为计算机编制的指令程序称为()。
【简答题】Compare the advantages and disadvantages of relational database and hierarchical database
【简答题】人们根据特定的需要预先为计算机编制的指令序列称为().A. A:软件 B. B:文件 C. C:程序 D. D:集合