题型:名词解释 设有关系R=(A,B,C)与SQL语句SELECT DISTINCT A,C FROM R WHEREB=5,则与之等价的关系代数表达式是( )。 Ⅰ.A,C(B=5(R)) Ⅱ.B=5(A,C(R))A.都等价B.仅ⅠC.仅ⅡD.都不等价 查看答案
题型:名词解释 –__________ will the meeting last? –Less than an hour.A.How farB.How soon C.How longD.How often 查看答案