4、单行函数—转换函数

To_char

参考文档：

http://baike.baidu.com/view/6011617.htm

select to_char(sysdate,'yyyy') from dual;

select to_char(sysdate,'fmyyyy-mm-dd') fromdual;

select to_char(sal,'L999,999,999') fromemp;

select to_char(sysdate,’D’) from dual;//返回星期

To_number

select to_number('13')+to_number('14') fromdual;

To_date

Select to_date(„20090210‟,‟yyyyMMdd‟) fromdual;