【单选题】关系模型中,主键是( )。
C.
可由一个或多个其值能惟一标识该关系模式中任何元组的属性组成
【单选题】I know my brother well. Once he has made up his mind, nothing can change it, but instead I usually ____.
【单选题】关系模型中,一个主键是( )。
C.
由一个或多个属性组成,其值能够唯一标识关系中实体。
【单选题】I know my job isn’t well paid, but ________ I don’t have to work long hours.
【单选题】—Do you know _____ does well in singing in your class? —My friend, I think. [ ]
【多选题】同一种内切酶产生的粘性末端片段连接时,会