4.转换函数:

---to_char
select to_char(hiredate,'yyyy-mm-dd') from emp
select to_char (hiredate,'yyyy"年"mm"月"dd"日"') from emp

select sal,to_char (sal,'l0,000,000.00') as saltest from emp

结果:

查询入职时间在1982年之后的员工:
select ename,hiredate from emp where hiredate>to_date('1981-12-31','yyyy-mm-dd')

查询工资大于2000的所有员工:
select ename,sal from emp where sal>to_number('¥2000','l9999');

5.通用函数: