【判断题】【消耗次数:1】
设 A={a,b,c,d}, A上的关系R1={,,},R2={,,,},则合成关系R1○R2等于:{,,}。
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错误
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【简答题】 设 A={a,b,c,d}, A上的关系R1={,,},R2={,,,},则合成关系R1○R2等于:[填空1]
【单选题】 设 A={a,b,c,d}, A上的关系R1={a,aa,bb,d},R2={a,db,cb,dc,b},则合成关系R2○R1等于:
①  {a,aa,ca,d
②  {c,d
③  {a,aa,ba,d
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【单选题】 设 A={a,b,c,d}, A上的关系R1={a,aa,bb,d},R2={a,db,cb,dc,b},则合成关系R1○R2等于:
①  {a,aa,ca,d
②  {c,d
③  {a,aa,ba,d
④  {b,cb,dc,b}.
【简答题】 设 A={a,b,c,d}, A上的关系R1={,,},R2={,,,},求合成关系R1○R2。
【单选题】 设关系R1具有a1个属性和b1个元组,关系R2具有a2个属性和b2个元组,则关系R1×R2所具有的属性个数为( )。
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【单选题】 在关系数据模型中,两个关系R1与R2之间存在1∶M的联系,可以通过在一个关系R2中的( )在相关联的另一个关系R1中检索相对应的记录。
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