T-SQL calculating percentage changes with nagative numbers

Posted on 2011-03-21
Medium Priority
Last Modified: 2012-05-11
my update statment did not get the correct result in the % changes column
Here is my example table:

table @t
score1st      smallint
score2nd      smallint
chagnes_%      dec(10, 4) -- I also try float

update statment

update t
 set changes_% = ( (score1st - score2nd) / score1st ) * 100
from @t t


score1st      score2nd   % CHANGES
20            20            0%
78            -20            125%
48            35            27%
24            66
17            19
56            38
30            -14
37            70            -89%
73            34
50            13
-20            57
50            20
53            -20
136            31
23            44
-4            220
56            52
56            54

Question by:jfreeman2010
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Author Comment

ID: 35182209
the result from the update statement show the %changes column are:

LVL 32

Expert Comment

by:Ephraim Wangoya
ID: 35182211

first it should be

(score2nd - score1st) / score1st ) * 100

what does a negative score mean

Author Comment

ID: 35182323
Its mean the score can be negative number.  those just a test number, I can name them as test1 and test1 as the column name.
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Author Comment

ID: 35182585
I fixed a problem by doing this:

( (score1st - score2nd) / nullif(convert(decimal(9,2),score1st,0) ) * 100
LVL 25

Accepted Solution

TempDBA earned 2000 total points
ID: 35182710
It is because when you are dividing the differnce with the score1st, the value coming out is 0.something. or somewholenumber.somenumber like 0.234, 1.2, 2.343,0.09,etc
Since this is smallint, the value obtained is the whole number i.e the first part not the full number.
Further multiplying it gives the wholenumber.

Instead of multiplying the number with 100 after the computation, do it like the following:
((score1st - score2nd)*100.0)/score1st

Author Comment

ID: 35183909

yes, it also works the way you suggested. thank you,

Author Closing Comment

ID: 35183911
very good!!

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