#执行下述程序后,print的输出是: def funname(x, y): print(y) x = 3 y = 4 funname(y, x)
拍照语音搜题,微信中搜索"皮皮学"使用
参考答案:
参考解析:
知识点:
皮皮学刷刷变学霸
举一反三
【单选题】What is the difference between a unique constraint and a primary key constraint?
A.
A unique key constraint requires a unique index to enforce the constraint,whereas a primary key constraint can enforce uniqueness using a unique key of or nonunique index
B.
A primary key column can be NULL,but a unique key column cannot be NULL
C.
A primary key constraint can use an existing index ,but a unique constraint always creates an index
D.
A unique constraint column can be NULL,but primary key columns can not be NULL