回复： Inconsistent results for division and multiplication operations

If the number of significant digits in the input is not fixed, it becomes challenging to achieve consistent results by rounding.
for example
postgres=# select round(1.003/1.002*5.01,2);
         ?column?
--------------------------
 5.01  
(1 row)

postgres=# select round(1.003*5.01/1.002,2);
      ?column?
--------------------
 5.02
(1 row)

szy
598546998(at)qq(dot)com

 

This is a common issue with using floating point math.  You will see the same issue with many systems.  Basically, the order of operations can trigger very minor differences in results, but if you round the first result to the same number of significant digits as the input, it would be identical.  https://learn.microsoft.com/en-us/office/troubleshoot/access/floating-calculations-info

On Mon, Nov 25, 2024 at 10:46 AM szy <598546998(at)qq(dot)com&gt; wrote:

Hi PostgreSQL community,

I have observed inconsistent results when performing division and multiplication operations in PostgreSQL.

postgres=# select 1.003/1.002*5.01;
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;?column?
--------------------------
&nbsp;5.0149999999999999999806&nbsp;&nbsp;
(1 row)

postgres=# select 1.003*5.01/1.002;
&nbsp; &nbsp; &nbsp; ?column?
--------------------
&nbsp;5.0150000000000000
(1 row)

However, the expected result should be consistent for both queries. The actual results differ

szy
598546998(at)qq(dot)com

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