2 个浮点值的总和给出了精度更高的不正确结果

Question

postgres 中 2 个浮点值的总和给出了更高精度的结果。 预计：

669.05 + 1.64 = 670.69

实际：

SELECT CAST(669.05 AS FLOAT) + CAST(1.64 AS FLOAT)
------------------
670.6899999999999

结果比预期的精度更高。

具有不同输入集的相同操作表现不同。

SELECT CAST(669.05 AS FLOAT) + CAST(1.63 AS FLOAT)
------------------
670.68

在这里，我通过找到存在问题的 2 个数字减少了问题陈述。实际问题是，当我在整个 table 上执行此操作时，结果会非常大且精度更高（取决于值，而且我没有准确解释精度拍摄的值 what/kind向上），我们必须处理应用程序级别的规模。示例查询

SELECT numeric_column_1/ CAST(numeric_column_2 AS FLOAT) FROM input_table;

注意：FLOAT(53) 的行为也相同。

Answer 1

根据 postgresql 文档，float 使用不精确的精度。最好使用 DECIMAL 或 NUMERIC，它们支持精确的用户指定精度。

SELECT CAST(669.05 AS numeric) + CAST(1.64 AS numeric)

Floating-Point Types in PostgreSQL

The data types real and double precision are inexact, variable-precision numeric types. On all currently supported platforms, these types are implementations of IEEE Standard 754 for Binary Floating-Point Arithmetic (single and double precision, respectively), to the extent that the underlying processor, operating system, and compiler support it.

数值类型

Name	Storage Size	Description	Range
smallint	2 bytes	small-range integer	-32768 to +32767
integer	4 bytes	typical choice for integer	-2147483648 to +2147483647
bigint	8 bytes	large-range integer	-9223372036854775808 to +9223372036854775807
decimal	variable	user-specified precision, exact	up to 131072 digits before the decimal point; up to 16383 digits after the decimal point
numeric	variable	user-specified precision, exact	up to 131072 digits before the decimal point; up to 16383 digits after the decimal point
real	4 bytes	variable-precision, inexact	6 decimal digits precision
double precision	8 bytes	variable-precision, inexact	15 decimal digits precision
smallserial	2 bytes	small autoincrementing integer	1 to 32767
serial	4 bytes	autoincrementing integer	1 to 2147483647
bigserial	8 bytes	large autoincrementing integer	1 to 9223372036854775807

DB Fiddle: Try it here

2 个浮点值的总和给出了精度更高的不正确结果

Summation of 2 floating point values gives incorrect result with higher precision

sql

postgresql

floating-point

casting

数值类型