更多"The kid is reaching () a bottle fro"的相关试题:
[单项选择]The kid is reaching ______ a bottle from the shelf when I came in.
A. to
B. at
C. for
D. in
[单项选择]设有关系R:(A,B,C) 与SQL语句select distinct A,C from R where B=5等价的关系代数表达式是
Ⅰ.πA.C(σB=5(R))
Ⅱ.σB=5(πA.C(R))
A. 都等价
B. 仅Ⅰ
C. 仅Ⅱ
D. 都不等价
[单项选择]课程表中有“课程号”、“课程名”、“授课老师”三个字段,SQL语句“SELECT*FROM课程WHERE课程名=''数据结构''”完成的操作称为
A. 选择
B. 投影
C. 连接
D. 并
[单项选择]设有关系R(A,B,C)和S(A,B,C),下面的SQL语句:
SELECT*FROM R WHERE A<=20
UNION
SELECT*FROM S WHERE A>=80
所对应的关系代数操作,除选择外还有( )操作。
A. 交
B. 差
C. 并
D. 笛卡尔积
[单项选择]SQL语句
SELECT 产地,COUNT(*)提供的商品种类数;
FROM 商品表;
WHERE 单价>200;
GROUP BY 产地HAVING COUNT(*)>=2;
ORDER BY 2 DESC
查询结果的第一条记录的产地和提供的商品种类数是 ______。
A. 北京,1
B. 上海,2
C. 广东,5
D. 广东,7
[单项选择]You can take anything from the shelf and read, but please ______ the books when you've finished with them.
A. put on
B. put down
C. put back
D. put off
[单项选择]设有关系R(A,B,C)和S(C,D)与SQL语句SELECT A,B,D FROM R,S WHERE R.C=S.C等价的关系代数表达式是