用于保存非常不同的小数位数的列类型

Question

我需要像这样存储数字

这是传感器数据，因此保持准确值很重要。有很多选择。

我的解决方案是将所有值乘以 100 万，并将它们存储为 bigint。这有意义吗？

Answer 1

这是有道理的，但我建议您只使用 decimal 数据类型：https://dev.mysql.com/doc/refman/5.7/en/precision-math-decimal-characteristics.html

如果您要乘以百万，并且如果您收到的数据集的小数点比您预期的多一位，您最终会将该数字乘以 1000 万，然后将所有其他数字乘以 10。相反，使用decimal 数据类型将为您提供小数点右边的 30 个数字。

The declaration syntax for a DECIMAL column is DECIMAL(M,D). The ranges of values for the arguments in MySQL 5.7 are as follows:

M is the maximum number of digits (the precision). It has a range of 1 to 65.

D is the number of digits to the right of the decimal point (the scale). It has a range of 0 to 30 and must be no larger than M.

和

The SQL standard requires that the precision of NUMERIC(M,D) be exactly M digits. For DECIMAL(M,D), the standard requires a precision of at least M digits but permits more. In MySQL, DECIMAL(M,D) and NUMERIC(M,D) are the same, and both have a precision of exactly M digits.

For a full explanation of the internal format of DECIMAL values, see the file strings/decimal.c in a MySQL source distribution. The format is explained (with an example) in the decimal2bin() function.

要格式化你的数字，你可以像这个答案描述的那样格式化：Format number to 2 decimal places

例子

create table test (
  price decimal(40,20)
);

-- all the above insertions will succeed cleanly
insert into test values (1.5), (1.66), (1.777), (1.12345678901234567890);

-- notice we have 21 digits after decimal
-- MySQL will insert data with 20 decimal and add a warning regarding data truncation
insert into test values (1.123456789012345678901);

数据

select * from test

price
1.50000000000000000000
1.66000000000000000000
1.77700000000000000000
1.12345678901234567890
1.12345678901234567890

select cast(price as decimal(40,2)) from test

price
1.50
1.66
1.78
1.12
1.12

用于保存非常不同的小数位数的列类型

Column type for saving very different number of decimals

mysql

decimal