下面的查询中哪一个会产生笛卡尔集（）A、SELECT e.empno，e.ename， e.deptno， d.deptno，d.loc  FROM  emp e，dept  d WHERE e.deptno=d.deptnoB、SELECT e.empno， e.ename， e.deptno， d.deptno，d.loc FROM emp  e，dept  dC、SELECT e.empno， e.ename， e.deptno， d.deptno，d.loc FROM emp e，dept d W

根据SQL标准，要查询表student中平均年龄age小于21的所在系dept及其平均年龄值，下面哪条语句适用?()

A select dept,avg(age) from student where avg(age)<21

B select dept,avg(age) from student group by dept having avg(age)<21

C select dept,avg(age) from student having avg(age)<21

D select dept,avg(age) from student group by dept where avg(age)<21

A.SELECT UNIQUE dept FROM staff

B.SELECT DISTINCT dept FROM staff

C.SELECT (dept) UNIQUE FROM staff

D.SELECT (dept) DISTINCT FROM staff

以下语句不正确的是( )

A.select * from emp;

B.select ename,hiredate,sal from emp;

C.select * from emp order deptno;

D.select * from where deptno=1 and sal<300;

A.SELECT TOP 5 * FROM EMP

B.SELECT DISTINCT 5 * FROM EMP

C.SELECT * FROM EMP WHERE ROWNUM<6

D.SELECT * FROM EMP WHERE ROWNUM=5

Examine the description of the EMPLOYEES table:EMP_ID NUMBER(4) NOT NULLLAST_NAME VARCHAR2(30) NOT NULLFIRST_NAME VARCHAR2(30)DEPT_ID NUMBER(2)JOB_CAT VARCHARD2(30)SALARY NUMBER(8,2)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;

A.select job from emp;

B.select job,count(*) from emp;

C.select distinct job,count(*) from emp;

D.select job,count(*) from emp group by job;

E.select job,sum(empno) from emp group by job;

A. DROP emp_dept_uv;

B. DELETE emp_dept_uv;

C. REMOVE emp_dept_uv;

D. DROP VIEW emp_dept_uv;

E. DELETE VIEW emp_dept_uv;

F. REMOVE VIEW emp_dept_uv;