SQL Percent difference between 2 aggregate columns

Question

I am unsure if my terminology is correct. I have this query:

select (select count(*)
        from table1
        where column1 = 'x' and column2 = 'y' and column3 = 'z'
       ) as new_column1,
       (select count(*) 
        from table 1
        where column1 = 'x' and column2 = 'y' and column3 = 'z'
       ) as new_column2;

I would like to find the percentage difference between the two new (aggregate?) columns. The original columns are varchar(2),two varchar(4) columns, and a varchar(3) column.

Answer 1

This will give you the delta between sum1 and sum2, expressed as a percentage relative to sum2:

select sum1      = s.sum1      ,
       sum2      = s.sum2      ,
       delta     = sum1 - sum2 ,
       delta_pct = 100.0 * ( sum1 - sum2 ) / sum2
from ( select sum1 = sum(case when t.c1='a' and t.c2='b' and t.c3='c' then 1 else 0 end) ,
              sum2 = sum(case when t.c1='x' and t.c2='y' and t.c3='z' then 1 else 0 end)
       from table1 t
     ) s

using the derived table in the from clause makes for cleaner, more readable SQL as you're not duplicating the aggregation expressions all over the place.

Answer 2

Here's one way you could do it:

select 
new_column1,
new_,
new_column1 / new_ * 100  as PercentDiff
from
(
    select (select count(*)
            from table1
            where column1 = 'x' and column2 = 'y' and column3 = 'z'
           ) as new_column1,
           (select count(*) 
            from table1
            where column1 = 'x' and column2 = 'y' and column3 = 'z'
           ) as new_
)

Answer 3

Change this to conditional aggregation:

select sum(case when column1 = 'x' and column2 = 'y' and column3 = 'z' then 1
                else 0
           end) new_column1,
       sum(case when column1 = 'x' and column2 = 'y' and column3 = 'z' then 1
                else 0
           end) new_column2,
       (sum(case when column1 = 'x' and column2 = 'y' and column3 = 'z' then 1.0
                 else 0.0
            end) /
        sum(case when column1 = 'x' and column2 = 'y' and column3 = 'z' then 1.0
                 else 0.0
            end)
       ) ratio
from table1;

Notice the use of decimal constants for the division. SQL Server does integer division on integers.