Acandidate key is().

A．an attribute or a set of attributes with a unique value for each tuple of a relation

B．a set of attributes referring to another relation in the database

C．an attribute or a set of attributes that is potentially the primary key of a relation

D．an attribute or a set of attributes that is potentially(有潜力地)the super key(超键)of a relation

[单选题]The key benefit of ( )is that it provides guidance and direction on how the project costs will be managed throughout the project.A．Plan Cost ManagementB．Control CostC．Estimate CostD．Determine Budget

[单选题]For relation where primary key contains multiple attributes， no non-key att

[单选题]The key word in Paragraph 4 is ______.A． barriersB． ignoranceC． disabilityD． prejudice

[单选题]There are a number of key technologies that will enable LTE Advanced to achieve the high data （ ） rates that are required．（ ） are two of the base technologies that will be enablers．Along with these there a number of other techniques and technologies

[名词解释] KEY-EL-EN

[名词解释] 主音（Key-note）

[填空题] key君是谁？（）

[名词解释] 主码（Primary Key）

[单选题]How many key comparisons are needed in searching for key value 38? (74) .(74) A．1B．4C．3D．2

[单选题]For relation where primary key contains multiple attributes，no non-key attribute should be functionally dependent on a part of primary key．This relation R is at least in (66) .(66) A．3NFB．2NFC．INFD．BCNF