给定关系模式R(A1，A2，A3，A4)，R上的函数依赖集F={A1A3→A2，A2→A3}，则R（ ）。若将R分解为ρ={(A1A2)，(A1，A3)}，那么该分解（此空作答）。
- A.是无损联接的
- B.是保持函数依赖的
- C.既是无损联接又保持函数依赖
- D.既是有损联接又不保持函数依赖
正确答案及解析
正确答案
解析
A1A3A4和A1A2A4可以推出其他全部属性，因此为候选关键字。设ρ1={A1，A2}，ρ2={A1，A3}，那么可得出：ρ1∩ρ2=A1，A1无法推出任何属性，所以是有损连接分解。原关系式里A1A3→A2，分解后的关系式并没有保存A2，所以该分解也不保持函数依赖。
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