选择题：
1)Which statement shows the maximum salary paid in each job category of each department?_______
A。 select dept_id， job_cat，max(salary) from employees where salary > max(salary);
B。 select dept_id， job_cat，max(salary) from employees group by dept_id，job_cat;
C。 select dept_id， job_cat，max(salary) from employees;
D。 select dept_id， job_cat，max(salary) from employees group by dept_id;
E。 select dept_id， job_cat，max(salary) from employees group by dept_id，job_cat，salary;
2)description of the students table:
sid_id number
start_date date
end_date date
which two function are valid on the start_date column?_________。
A。 sum(start_date)
B。 avg(start_date)
C。 count(start_date)
D。 avg(start_date，end_date)
E。 min(start_date)
F。 maximum(start_date)
3)for which two constraints does the oracle server implicitly create a unique index?______。
A。 not null
B。 primary
C。 foreign key
D。 check
E。 unique
4)in a select statement that includes a where clause，where is the group by clause placed in the select statement?______。
A。 immediately after the select clause
B。 before the where clause
C。 before the from clause
D。 after the order by clause
E。 after the where clause
5)in a select statement that includes a where clause，where is the order by clause placed in the select statement?______。
A。immediately after the select clause
B。before the where clause
C。after all clause
D。after the where clause
E。before the from clause
6)evaluate there two sql statements______。
Select last_name，salary from employees order by salary;
Select last_name，salary from employees order by 2 asc;
A。the same result B。different result C。the second statement returns a syntax error
7) you would like to display the system date in the format20051110 14：44：17。Which select statement should you use?______。
A。 select to_date(sydate，’yearmmdd hh:mm:ss’)from dual;
B。 select to_sydate，’yearmonthday hh:mi:ss’)from dual;
C。 select to_date(sydate，’yyyymmdd hh24:mi:ss’)from dual;
D。 select to_sydate，’yyyymmdd hh24:mi:ss’)from dual;
E。 select to_sydate，’yy-mm-dd hh24:mi:ss’)from dual;
8)which select statement will the result ‘ello world’from the string‘Hello world’?______。
A。 select substr(‘Hello World’，1)from dual;
B。 select substr(trim(‘Hello World’，1，1))from dual;
C。 select lower(substr(‘Hello World’，1))from dual;
D。 select lower(trim(‘H’from‘Hello World’))from dual;
9)which are DML statements(choose all that apply)______。
Amit B。merge C。D。 E。creat F。drop
10)Select 语句中用来连接字符串的符号是___C___。
A。 + B。 & C。|| D。|