Question

我使用以下查询;

select round(sum(quantity * calories)) as calories
from tableName;

其中数量和卡路里的类型为double，其值为1.00＆amp;分别为110.50。我期待输出为111，但上面的查询却给了我110.但如果我执行如下的简单查询，

select round (110.50);

它给我111作为输出。我浏览了这个Link，并使用了如下的查询;

select round(sum(cast(quantity * calories as char))) as calories
from tableName;

但是这个也不适用于我并且输出110作为输出。有人能说出如何达到所需的111输出？

Answer 1

TRY :::

SELECT ROUND ( CAST ( SUM (quantity * calories) AS DECIMAL(10,4))) AS calories
FROM tableName;

Answer 2

使用浮点数进行计算时，最好使用decimal（m，d）数据类型而不是float / double，因为float和double都表示近似数值数据值，并且在计算时使用时容易出现舍入错误。

您的查询可以使用：

select round(cast(sum(quantity * calories) as decimal(8,1))) as calories
from tableName;

Answer 3

您可以先将参数转换为DECIMAL来完成此操作。然后我们将SUM / ROUND操作作为DECIMAL执行。

SELECT round( sum( 
    CAST(quantity AS DECIMAL(10,4)) * 
    CAST(calories AS DECIMAL(10,4)) ) ) AS calories
FROM tableName;

<强>样品

mysql> SELECT * FROM tableName;

+----+----------+----------+
| id | quantity | calories |
+----+----------+----------+
|  1 |        1 |    110.5 |
+----+----------+----------+
1 row in set (0,02 sec)

mysql> SELECT round( sum(
    ->     CAST(quantity AS DECIMAL(10,4)) *
    ->     CAST(calories AS DECIMAL(10,4)) ) ) AS calories
    -> FROM tableName;
+----------+
| calories |
+----------+
|      111 |
+----------+
1 row in set (0,00 sec)

mysql>

样本2与DECIMAL（10,2）

mysql> SHOW CREATE TABLE tableName\G
*************************** 1. row ***************************
       Table: tableName
Create Table: CREATE TABLE `tableName` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `quantity` decimal(10,1) DEFAULT NULL,
  `calories` decimal(10,2) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8
1 row in set (0,00 sec)

mysql> SELECT * from tableName;
+----+----------+----------+
| id | quantity | calories |
+----+----------+----------+
|  1 |      1.0 |   110.50 |
+----+----------+----------+
1 row in set (0,00 sec)

mysql> select round(sum(quantity * calories)) as calories
    -> from tableName;
+----------+
| calories |
+----------+
|      111 |
+----------+
1 row in set (0,00 sec)

mysql>

MySQL round（）与sum（）无法正常工作

3 个答案: