Oracle 取整、四舍五入及格式化 Round/Floor/Ceil

原文地址：http://kb.cnblogs.com/a/1552790/

SELECT ROUND( number, [ decimal_places ] ) FROM DUAL

说明：

number : 将要处理的数值

decimal_places : 四舍五入，小数取几位,不填默认为0

Sample :

select round(123.456) from dual;              结果： 123
select round(123.456, 0) from dual;          结果： 123
select round(123.456, 1) from dual;          结果： 123.5
select round(123.456, 2) from dual;          结果：123.46
select round(123.456, 3) from dual;          结果： 123.456
select round(-123.456, 2) from dual;         结果：-123.46

取整（向下取整）：

select floor(5.534) from dual;
select trunc(5.534) from dual;

上面两种用法都可以对数字5.534向下取整，结果为5.
如果要向上取整 ，得到结果为6，则应该用ceil

select ceil(5.534) from dual;

保留N位小数（不四舍五入）：

select trunc(5.534,0) from dual;
select trunc(5.534,1) from dual;
select trunc(5.534,2) from dual;

结果分别是 5,5.5,5.53，其中保留0位小数就相当于直接取整了。

数字格式化：

select to_char(12345.123,'99999999.9999') from dual;

结果为12345.123

select to_char(12345.123,'99999999.9900') from dual;

小数后第三第四为不足补0，结果为12345.1230

select to_char(0.123,'99999999.9900') from dual;
select to_char(0.123,'99999990.9900') from dual;

结果分别为 .123, 0.123

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