A.select * from emp where comm=null;B.select * from emp where comm is not null;C.select * from emp where comm <>null;D.select * from emp where comm is null;请帮忙给出正确答案和分析,谢谢!
A.select ename,sal,comm from emp where sal>=2500 or sal<=4000; B.select ename,sal,comm from emp where sal>=2500 and salz<=4000; C.select ename,sal,comm from emp where sal between 2500 or 4000; D.select ename,sal,comm from emp where sal between 2500 and 4000; ...