单项选择题
将两个SELECT语句各自得到的结果集并为一个集,并删除重复元组的集合操作是_______。 A.
UNION B.
UNION AL C.
INTERSECT D.
MINUS
将两个SELECT语句各自得到的结果集并为一个集,并删除重复元组的集合操作是_______。 A.
UNION B.
UNION AL C.
INTERSECT D.
MINUS
你可能感兴趣的试题
单项选择题
The governments, environmental protection departments and enterprises of China have legal responsibilities and obligations for the emergency management of environmental emergencies. The legal responsibilities of the governments do not include ( )
The governments, environmental protection departments and enterprises of China have legal responsibilities and obligations for the emergency management of environmental emergencies. The legal responsibilities of the governments do not include ( )
A．Timely report to relevant companies involved in environmental emergencies
B．Carry out monitoring and early warning, and take effective emergency response measures when environmental emergencies occur
C．Post-evaluation and reconstruction
D．Develop emergency plan, establish emergency training and carry out emergency drill