表emp有如下字段：deptno, empid, name, job, sal。分别表示：部门编号、员工编号、员工姓名、职位、薪资。求每个部门的工资占比，结果用百分号表示，保留2位小数。以下代码正确的是（ ）

A.    select deptno, sum(sal)/(select sum(sal) from emp) from emp;

B.    select deptno, sum(sal)/(select sum(sal) from emp) from emp group by deptno;

C.    select deptno, concat(round(sum(sal)/(select sum(sal) from emp)*100,2),“%”) from emp group by deptno;

D.    select deptno, concat(round(sum(sal)/(select sum(sal) from emp),2),“%”) from emp group by deptno;
参考答案： C
解析：难度中上。分组后部门薪资总和占比为sum(sal)/(select sum(sal) from emp)以小数形式呈现；round(sum(sal)/(select sum(sal) from emp)*100,2)实现该值扩大100倍，保留2位小数；concat(round(sum(sal)/(select sum(sal) from emp)*100,2),“%”) 实现该值与“%”拼接。