【判断题】投影运算之后不仅取消了原关系中的某些列,而且可能会取消某些元组。
【单选题】Taiwan lies _____ the east of Fujian. [ ]
【单选题】患者男,69岁,血栓闭塞性脉管炎出现间歇性跛行,主要原因是
【单选题】使用力的平行四边形法则、三角形法则、多边形法则的前提条件是( )
【单选题】In previous times, when fresh meat was inadequate, pigeons were kept by many households as a source of food.
【单选题】Taiwan lies ______the southeast of China. [ ]
【单选题】Taiwan lies ______ the southern coast of China, and it’s really _____ island. Is that so
【单选题】由于岩石的抗压强度远大于它的抗拉强度,所以岩石属于( )
【简答题】Taiwan lies ______the southeast of China. A. in B. on C. to
【判断题】投影运算不仅取消了原关系中的某些列,而且可能会减少元组。