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; 四舍五入 SELECT round(5.534) FROM dual; SELECT round(5.534,0) FROM dual; SELECT round(5.534,1) FROM dual; SELECT round(5.534,2) FROM dual; 结果分别为 6, 6, 5.5, 5.53 保留N位小数（不四舍五入）按位数截取 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
