Re: Queries on doubles are not stable - Thimble Smith - com.mysql.lists.bugs

4 messages in com.mysql.lists.bugsRe: Queries on doubles are not stable

From	Sent On	Attachments
Alan G. Carter	30 Nov 2000 14:11
Sasha Pachev	01 Dec 2000 16:49
Thimble Smith	02 Dec 2000 09:59
Michael Widenius	03 Dec 2000 02:35

Subject:	Re: Queries on doubles are not stable
From:	Thimble Smith (ti...@mysql.com)
Date:	12/02/2000 09:59:40 AM
List:	com.mysql.lists.bugs

On Fri, Dec 01, 2000 at 05:49:45PM -0700, Sasha Pachev wrote:

On Thursday 30 November 2000 15:11, Alan G. Carter wrote:

/usr/local/mysql/bin/mysql -v -u root --password=$1 << EOF use mysql create table test_doubles (datum double);

insert into test_doubles values (0.5); insert into test_doubles values (1.0); insert into test_doubles values (1.5); insert into test_doubles values (2.0); insert into test_doubles values (2.5);

select * from test_doubles; select * from test_doubles where datum < 1.5; select * from test_doubles where datum > 1.5; select * from test_doubles where datum = 1.5; # # What happens with the bug is: # # 1) 5 rows # 2) 5 rows # 3) 0 rows # 4) 1 rows

The problem with double comparisons is that there is always a margin of error.

This would explain the problem if it were row 4 which were "incorrect". But it doesn't explain rows 2 and 3 being wrong.

Alan, I'm not aware of any changes between 3.23.25 and the current code that pertain to this - nor have I heard of this problem in 3.23.25 from anyone else. So, I'm not sure what is making the difference....

Tim