吉大20春学期《数据库应用技术》在线作业一-0001
试卷总分:100
一、单选题(共25 道试题,共100 分)
1.Given the tables: COUNTRY STAFF id name person cities id name 1 Argentina 1 10 1 Aaron 2 Canada 2 20 2 Adams 3 Cuba 2 10 3 Jones 4 Germany 1 0 5 France 3 5 6 Italy 1 5 the report: id name number_of_countries ---------- ---------- ------------------- 1 Aaron 3 and the SQL statement: SELECT B.id,https://www.doczj.com/doc/1915671772.html,,COUNT(DISTINCT https://www.doczj.com/doc/1915671772.html,) AS number_of_countries FROM country A, staff B WHERE B.id=A.person GROUP BY B.id,https://www.doczj.com/doc/1915671772.html, HA VING COUNT(DISTINCT https://www.doczj.com/doc/1915671772.html,)>:count_var Which of the following values does :count_var require to print out the above report?
A.1
B.2
C.3
D.4
正确答案:B
2.两个子查询的结果（），可以执行并、交、差操作
A.结构完全一致
B.结构完全不一致
C.结构部分一致
D.主键一致
正确答案:A