在SQL中,可以用谓词UNIQUE来测试一个集合是否______。A.为空集合 B. 发布时间:2017-06-12 12:55 │ 来源:www.tikuol.com 题型:单项选择题 问题: 在SQL中,可以用谓词UNIQUE来测试一个集合是否______。A.为空集合B.存在重复分量值C.为非空集合D.存在重复元组
题型:单项选择题 All possible means ____, but nothing can prevent the buildings ____.[ ]A. has tried; from being pulled down B. have tried; from pulling downC. has been tried; from pulling down D. have been tried; from being pulled down 查看答案