Question

我有这张表的订单

+-----+--------+--------+-----------+-----------+
|   id|order_id|   price|        tax|       qty |
+-----+--------+--------+-----------+-----------+
|    5|     123|  231.40|      50.91|          1|
+-----+--------+--------+-----------+-----------+
|    6|     123|  210.74|      46.36|          1|
+-----+--------+--------+-----------+-----------+

此查询用于获取订单123的结果

SELECT Sum(price * qty)               AS tot_sub,
       ( Sum(( price + tax ) * qty) ) AS tot
FROM   products
WHERE  order_id = 123

这就是结果

+-------+-----------------+
|tot_sub|tot              |
+-------+-----------------+
|442.14 |539.4100000000001|
+-------+-----------------+

我期待tot（539.41）的完美价值

我知道浮点数的内部表示（通常）可能有一些错误，并且与确切的理论数不同。

在这种情况下，如果不使用ROUND函数，我可以编写更好的查询来避免此错误吗？

感谢

Answer 1

使用cast as decimal。

更改：

SELECT Sum(price * qty) AS tot_sub,
       ( Sum(( price + tax ) * qty) ) AS tot
FROM   products
WHERE  order_id = 123

致：

SELECT Sum(price * qty) AS tot_sub,
       Sum( ( cast( price as decimal(10,2) ) 
            + cast( tax   as decimal(10,2) ) ) * qty ) AS tot
FROM   products
WHERE  order_id = 123

请参阅 ：

MySQL: CAST(expr AS type)
- CAST（）函数接受任何类型的表达式，并生成指定类型的结果值。

Answer 2

SELECT Sum(price * qty)               AS tot_sub,
       Round( Sum(( price + tax ) * qty) ),2) AS tot
FROM   products
WHERE  order_id = 123

mysql舍入错误和聚合函数

2 个答案: