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 format“20051110 14：44：17”。which select statement should you use?______。
a. select to_date(sydate,’yearmmdd hh:mm:ss’)from dual;
b. select to_char(sydate,’yearmonthday hh:mi:ss’)from dual;
c. select to_date(sydate,’yyyymmdd hh24:mi:ss’)from dual;
d. select to_char(sydate,’yyyymmdd hh24:mi:ss’)from dual;
e. select to_char(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)______.
a.commit  b.merge   c.update  d.delete e.creat  f.drop

10)select 语句中用来连接字符串的符号是______.
a. “+”   b. “&” c.“||” d.“|”

问答题： 什么是聚集索引，什么是非聚集索引，什么又是主键？