Question

In all other languages (arithmetic engines in general) putting an extra set of parenthesis around operators of same priority does not impact results. But recently in a testing project I noticed that MS SQL server changes the results in those cases. Please take a look at the query below, and let me know if you have any idea (or a setting in SQL Server administration) or any links to MSDN article explaining the behavior.

select (0.55 * 287.61 / 0.66) calc_no_parens
,(0.55 * (287.61 / 0.66)) calc_parens
,round(0.55 * 287.61 / 0.66,2) no_paren_round
,round(0.55 * (287.61 / 0.66),2) paren_round;

Results

Column  Record 1
calc_no_parens  239.6750000
calc_parens     239.67499985
no_paren_round  239.6800000
paren_round     239.67000000

To me, first two of them should return 239.675, and round should give 239.68.

Answer 1

You will get the desired result if you declare each value as Float.

DECLARE @Float1 float, @Float2 float, @Float3 float;
SET @Float1 = 0.55;
SET @Float2 = 287.61;
SET @Float3 = 0.66;

select (@Float1 * @Float2 / @Float3) calc_no_parens
,(@Float1* (@Float2/ @Float3)) calc_parens
,round(@Float1 * @Float2/ @Float3,2) no_paren_round
,round(@Float1* (@Float2/ @Float3),2) paren_round;

Output

calc_no_parens  calc_parens no_paren_round  paren_round
239.675          239.675    239.68           239.68

You may want to see this article: So-called “exact” numerics are not at all exact!