ROUND()
函数说明
ROUND() 函数返回了某个数字在特定位数四舍五入后的数值。
该函数返回指定位数上最接近的数字。如果给定的数字与周围的数字距离相等（比如为 5），那么将采用“banker's rounding”（银行进位法）的方式进行舍入。
函数语法
> ROUND(number, decimals)
> ROUND(number)
参数释义
| 参数 | 说明 |
|---|---|
| number | 必要参数，想要进行舍入的数值，可取任意数值数据类型 |
| decimals | 可选参数，表示将要舍入的小数点后的位数。默认值为 0，代表舍入到整数。 decimals>0 函数将舍入到小数点后的位数 decimals<0 函数将舍入到小数点前的位数 decimals=0 函数将舍入到整数 |
示例
drop table if exists t1;
create table t1(a int ,b float);
insert into t1 values(1,0.5);
insert into t1 values(2,0.499);
insert into t1 values(3,0.501);
insert into t1 values(4,20.5);
insert into t1 values(5,20.499);
insert into t1 values(6,13.500);
insert into t1 values(7,-0.500);
insert into t1 values(8,-0.499);
insert into t1 values(9,-0.501);
insert into t1 values(10,-20.499);
insert into t1 values(11,-20.500);
insert into t1 values(12,-13.500);
mysql> select a,round(b) from t1;
+------+----------+
| a | round(b) |
+------+----------+
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 20 |
| 5 | 20 |
| 6 | 14 |
| 7 | -0 |
| 8 | -0 |
| 9 | -1 |
| 10 | -20 |
| 11 | -20 |
| 12 | -14 |
+------+----------+
12 rows in set (0.00 sec)
mysql> select a,round(b,-1) from t1;
+------+--------------+
| a | round(b, -1) |
+------+--------------+
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 20 |
| 5 | 20 |
| 6 | 10 |
| 7 | -0 |
| 8 | -0 |
| 9 | -0 |
| 10 | -20 |
| 11 | -20 |
| 12 | -10 |
+------+--------------+
12 rows in set (0.01 sec)
mysql> select round(a*b) from t1;
+--------------+
| round(a * b) |
+--------------+
| 0 |
| 1 |
| 2 |
| 82 |
| 102 |
| 81 |
| -4 |
| -4 |
| -5 |
| -205 |
| -226 |
| -162 |
+--------------+
12 rows in set (0.01 sec)