关于to_number和to_char函数
to_number是将字符串按照指定的格式专为数字，相反，to_char是将数字转换为指定格式的字符串。
select to_char(1/7,'999,990.99') from dual;--正常select to_number('19.43453','99999999.99') from dual;--报错，无效字符select to_number('0.43453','99999990.99') from dual;--报错，无效字符select to_number('19.43453','99999999.99999999') from dual;--正常select round(1/7,4) from dual;?oracle order by number/char 数字?
?如果是字符串则不会按顺序