MySQL 对 FLOAT 数据使用 SUM
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Using SUM on FLOAT data
提问by Emanuil Rusev
One table:
items(id, price)
一张表：
items(id, price)
Has one row:
id: 1, price: 565.8
有一行：
id：1，价格：565.8
SELECT price FROM itemsgives 565.8SELECT SUM(price) FROM itemsgives 565.799987792969instead of 565.8which I'd expect.
SELECT price FROM items给565.8SELECT SUM(price) FROM items给565.799987792969，而不是565.8我所期待。
Where does the 565.799987792969come from?
在什么地方565.799987792969来的呢？
采纳答案by LittleBobbyTables - Au Revtheitroad
I'm not sure what version you are using, but it sounds like this linkdescribes what you are experiencing.
我不确定您使用的是哪个版本，但听起来此链接描述了您所遇到的情况。
From the link:
从链接：
mysql> select * from aaa;
+----+------------+------+
| id | month_year | cost |
+----+------------+------+
| 1 | 2002-05-01 | 0.01 |
| 2 | 2002-06-01 | 1.65 |
| 3 | 2002-07-01 | 0.01 |
| 4 | 2002-01-01 | 0.01 |
+----+------------+------+
mysql> select id, sum(cost) from aaa group by id;
+----+---------------------+
| id | sum(cost) |
+----+---------------------+
| 1 | 0.00999999977648258 |
| 2 | 1.64999997615814 |
| 3 | 0.00999999977648258 |
| 4 | 0.00999999977648258 |
+----+---------------------+
The SUM function changes 0.01 to 0.00999999977648258.
Floating point numbers are stored as approximate values; if you are storing a price, you are better off using a decimal datatype which stores precise values.
浮点数存储为近似值；如果您要存储价格，最好使用存储精确值的十进制数据类型。
