select empno,ename, case when sal<1000 then ‘low‘ when sal>=1000 and sal <3000 then ‘middle‘ else ‘high‘ end as new_sal from emp;
select empno,ename, case when comm is null then 0 else comm end from emp;
select empno,ename,cast(sal as string) new_sal from emp；
原文：https://www.cnblogs.com/zhange000/p/10469607.html