這是去年的題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 numberstart_date dateend_date datewhich two function are valid on the start_date column?_________。(start_date)(start_date)(start_date)(start_date,end_date)(start_date)(start_date)3)for which two constraints does the oracle server implicitly create a unique index?______。A. not nullB. primaryC. foreign keyD. checkE. unique4)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 clauseB. before the where clauseC. before the from clauseD. after the order by clauseE. after the where clause5)in a select statement that includes a where clause,where is the order by clause placed in the select statement? after the select the where all the where the from clause6)evaluate there two sql last_name,salary from employees order by salary;Select last_name,salary from employees order by 2 asc; same result result second statement returns a syntax error7) 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’?. 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) )Select 語句中用來連接字符串的符號是. “+” B. “&” C.“||” D.“|”問答題： 什么是聚集索引，什么是非聚集索引，什么又是主鍵？