已知关系模式R(A,B,C,D,E)及其上的函数相关性集合F={A→D,B→C ,E→A },该关系模式的候选关键字是。
查看答案
设有关系模式R(A,B,C,D),其上的函数依赖集:F={A→C,C→A,B→AC,D→AC}(1).计算(AD)+。(2).求F的最小等价依赖集Fmin。
设有关系模式R(U,F),其中:U={E,F,G,H},F={E→G,G→E,F→EG,H→EG,FH→E}求F的最小依赖集。
设有关系模式R(U,F),其中 :属性集U为ABC,函数依赖集 F={A→BC,B→C,A→B,AB→C}( 1 ) 计算A+( 2 ) 求 F 的最小等价依赖集 Fmin
1.A heavy flood caused the bridge to ____ ; now, no one can cross the river without boats.2.Susan has been crying a lot since her sister died a year ago; it seems that she could never ____from the heavy loss.3.It's sometimes considered bad manners to ____ on the table while eating, so please be careful not to do so.4.After crying for some time, she looked at her face ____ in the mirror, only to find she was such a sad and plain-looking girl.5.I had to hold tightly the handrails (扶手) along the hall to keep myself from losing my balance on the ____floor.6. The man phoned the police and later went to the police station to look at photos to____ the robbers.7. The imperial examination system, which started in the Sui Dynasty, was ____in 1905.8. Many smokers choose to ____the fact that smoking is harmful to health and refuse to stop smoking.9. He no longer had a(n) ____ for further education because he thought the costs were too high.10. Although she often seemed quite cold and strict, her smiling eyes____ her true nature.