[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"$fPtKKC9pvKnH0nNJ7DjO8rduoerB-lM3drdzxN9gklQk":3},{"answer":4,"createTime":5,"id":6,"options":7,"origin":12,"question":19,"related":20,"source":30,"type":31},[],"2025-03-12 12:55:40",178941236,[8,9,10,11],"7和8","7和15","12和8","12和15",{"count":13,"courseId":14,"courseImg":15,"courseName":16,"workId":17,"workName":18},16,"d57bc649e6d0506b2d28e9996a759039","https:\u002F\u002Ftihai-oss-cloud.itihey.com\u002Fimg\u002F7e2d5ad53be3d12aacc56ee37db405b7.jpg","数据库原理与应用","work_41177471","第二章作业","如果关系R中有4个属性和3个元组,关系S中有 3个属性和5个元组,则R*S的属性个数和元组个数分别是( )",[21,32,35,44,53,62,71,80,89,98],{"answer":22,"createTime":5,"id":23,"options":24,"question":29,"source":30,"type":31},[],178941235,[25,26,27,28],"交","并","笛卡尔积","连接","如图所示,两个关系 R1和 R2,它们进行( )运算后得到 R3. R1 R2 \u003Cimg src=\"https:\u002F\u002Ftihai-oss-cloud.itihey.com\u002Fimg\u002Ffa291ea265bc9ca1a9cbdf4e90e7dca3.png\">\u003Cimg src=\"https:\u002F\u002Ftihai-oss-cloud.itihey.com\u002Fimg\u002F268c41a9749a4c1891e300b20a5b7350.png\"> R3 \u003Cimg src=\"https:\u002F\u002Ftihai-oss-cloud.itihey.com\u002Fimg\u002Fd9f6151253dc5534156b4b365202aceb.png\">","v1",0,{"answer":33,"createTime":5,"id":6,"options":34,"question":19,"source":30,"type":31},[],[8,9,10,11],{"answer":36,"createTime":5,"id":37,"options":38,"question":43,"source":30,"type":31},[],178941237,[39,40,41,42],"T= R∩S","T= R∪S","T= R×S","T= R÷S","\u003Cimg src=\"https:\u002F\u002Ftihai-oss-cloud.itihey.com\u002Fimg\u002Fbb66e3ec2941c9fce8648326cf718c61.png\">\u003Cimg src=\"https:\u002F\u002Ftihai-oss-cloud.itihey.com\u002Fimg\u002Fea8a69856ec3e3d4bb58dad1f04200d1.png\">\u003Cimg src=\"https:\u002F\u002Ftihai-oss-cloud.itihey.com\u002Fimg\u002F93c0c508eebb4c306aa34e4f58b4c2ea.png\"> 下列操作正确的是( )",{"answer":45,"createTime":5,"id":46,"options":47,"question":52,"source":30,"type":31},[],178941238,[48,49,50,51],"每个关系中可以有两个主码","主码的值不能为空值","主码的值不能有重复","能唯一标识元组的一个属性或属性集","关于关系数据库中的主码,描述错误的是( )",{"answer":54,"createTime":5,"id":55,"options":56,"question":61,"source":30,"type":31},[],178941239,[57,58,59,60],"相同的属性个数","相同的属性","相同的元组","相同的主键","进行自然连接运算的两个关系必须有( )",{"answer":63,"createTime":5,"id":64,"options":65,"question":70,"source":30,"type":31},[],178941240,[66,67,68,69],"取列运算","投影运算","连接运算","选择运算","取出关系中的某些列,并消去重复元组的关系代数运算称为( )",{"answer":72,"createTime":5,"id":73,"options":74,"question":79,"source":30,"type":31},[],178941241,[75,76,77,78],"小于","小于或等于","等于","大于","在关系代数中,对一个关系做投影操作后,新关系的元组个数( )原来关系的元组个数",{"answer":81,"createTime":5,"id":82,"options":83,"question":88,"source":30,"type":31},[],178941242,[84,85,86,87],"实体完整性","参照完整性","用户自定义完整性","键完整性","在关系数据库中,关系与关系之间的联系是通过( )",{"answer":90,"createTime":5,"id":91,"options":92,"question":97,"source":30,"type":31},[],178941243,[93,94,95,96],"实体完整性约束","参照完整性约束","用户自定义完整性约束","键完整性约束","在学生关系中,规定学号的值域是由8个数字组成的字符串,其规则属于( )",{"answer":99,"createTime":5,"id":100,"options":101,"question":106,"source":30,"type":31},[],178941244,[102,103,104,105],"σgtype='电器'(Πgname,gstock(Goods))","Πgname,gstock(σgtype='电器'(Goods))","σgname,gstock(σgtype='电器'(Goods))","Πgname,gstock(Πgtype='电器'(Goods))","设商品关系模式为:商品(商品编号gid,商品名称gname,商品类型gtype,型号model,库存量gstock,单价gprice,商品描述gdescribe),则"从商品中查询商品类型为电器的商品名称及库存量"的关系代数式是( )"]