Division with Aggregate Functions in SQL Not Behaving as Expected - sql

Question

I'm trying to do some crosstabs in SQL Server 2008 R2. That part is alright, however, if I try to get percentages for each cell, I run into a problem.
Here is a distilled use case: A survey where people give their favorite color and their favorite fruit. I'd like to know how many like a given fruit AND a given color:
with survey as (
select 'banana' fav_fruit, 'yellow' fav_color
union select 'banana', 'red'
union select 'apple', 'yellow'
union select 'grape', 'red'
union select 'apple', 'blue'
union select 'orange', 'purple'
union select 'pomegranate', 'green'
)
select
s.fav_color,
sum(case
when s.fav_fruit = 'banana' then 1
else 0
end) as banana,
sum(case
when s.fav_fruit = 'banana' then 1
else 0
end) / sum(1) -- why does division always yield 0? "+", "-", and "*" all behave as expected.
* 100 as banana_pct,
sum(1) as total
from
survey s
group by
s.fav_color;
Results:
fav_color banana banana_pct total
------------------------------------
blue 0 0 1
green 0 0 1
purple 0 0 1
red 1 0 2
yellow 1 0 2
What I was expecting:
fav_color banana banana_pct total
------------------------------------
blue 0 0 1
green 0 0 1
purple 0 0 1
red 1 50 2
yellow 1 50 2
Please help me to get what I was expecting?

Answer 1

You are using SQL Server. Here is a much simpler example that replicates the issue:
select 1/2
SQL Server does integer division.
Replace the denominator with something like sum(1.0) or sum(cast 1 as float) or sum(1e0) instead of sum(1).
Contrary to my expectation at least, SQL Server stores numbers with decimal points as numeric/decimal type (see here) rather than float. The fixed number of decimal spaces might affect subsequent operations.

Answer 2

Query:
SQLFIddleexample
SELECT s.fav_color,
sum( CASE WHEN s.fav_fruit = 'banana' THEN 1 ELSE 0 END ) AS banana,
sum( CASE WHEN s.fav_fruit = 'banana' THEN 1 ELSE 0 END) / sum(1.00) -- why does division always yield 0? "+", "-", and "*" all behave as expected.
* 100 AS banana_pct,
sum(1) AS total
FROM survey s
GROUP BY s.fav_color
Result:
| FAV_COLOR | BANANA | BANANA_PCT | TOTAL |
-------------------------------------------
| blue | 0 | 0 | 1 |
| green | 0 | 0 | 1 |
| purple | 0 | 0 | 1 |
| red | 1 | 50 | 2 |
| yellow | 1 | 50 | 2 |

Answer 3

I've recently discovered the IIF function. It makes things much cleaner. Taking Justin's example from above:
SELECT s.fav_color,
sum( IIF(s.fav_fruit = 'banana', 1,0) AS banana,
sum( IIF(s.fav_fruit = 'banana', 1,0) / sum(1.00)
* 100 AS banana_pct,
sum(1) AS total
FROM survey s
GROUP BY s.fav_color