设R和S是两个关系，与关系代数表达式RXS等价的SQL语句是 【8】 。
参考答案：SELECT*FROM R，S或SELECTR.*，S.* FROM R，S
解析：[命题目的] 本题考查笛卡尔积的集合运算。
[解题要点] R×S表示求关系R和S笛卡尔积，是一个元数为两关系元数之和的元组集合，每一元组前部分为R关系的元组各属性值，后部分为S关系元组的各属性值，所以对应的SQL语句应为SELECT*FROMR，S。
阅读并排序 下面的短文由六个段落组成，开头和结尾已给出，其余的四个段落均是随机排列的。请根据段落之间的逻辑关系，用字母A、B、C、 D重新排列这四个段落的顺序，使短文通顺。
小题2:His father died when he was just 12 years old and Clemens then went to work for a printer to help support his family. He traveled around, and worked in many different cities. 小题3:In 1865,Clemens wrote a story about a jumping frog with his pen-name. The story and the writer became famous. After that, he wrote many books, including The Adventures of Tom Sawyer. It was published in 1876. He also gave many lectures, and became a very famous and popular man. 小题4:Clemens moved around the USA on the steamboat, and tried several jobs. He was a soldier, and a silver miner. And then he started working as a writer for a newspaper. At this time, he decided to use a pen-name for his stories, and he chose the name "Mark Twain". Samuel Clemens died in 1910. He is considered to be one of the greatest writers in American history |