Do math operations to output from COUNT and GROUP BY statemetns - sql

Question

Suppose I have a Yes/No data column. Then I can count the observations in each outcome category by
Select MyVar, count(MyVar) from MyTable
group by MyVaR;
The output is someting like:
MyVar count(MyVar)
Yes 10
No 5
How can I add another element to this outputtable which is the fraction (Yes/No) so my final table is something like:
MyVar count(MyVar)
Yes 10
No 5
Fraction 2
Is there a simple solution to this?

Answer 1

You can use group by grouping sets() for that:
Select
case
when grouping(MyVar)=0 then MyVar
else 'Fraction'
end grouping_value,
case
when grouping(MyVar)=0 then count(MyVar)
else count(decode(MyVar,'Yes',1)) / count(decode(MyVar,'No',1))
end c
from MyTable
group by grouping sets(MyVaR,())
Full test case with sample data:
with MyTable(MyVar) as (
select *
from table(sys.odcivarchar2list(
'Yes','Yes','Yes','Yes','Yes','Yes','Yes','Yes','Yes','Yes',
'No','No','No','No','No'
))
)
Select
case
when grouping(MyVar)=0 then MyVar
else 'Fraction'
end grouping_value,
case
when grouping(MyVar)=0 then count(MyVar)
else count(decode(MyVar,'Yes',1)) / count(decode(MyVar,'No',1))
end val
from MyTable
group by grouping sets(MyVaR,())
;
Results:
GROUPING_VALUE VAL
--------------- ----------
No 5
Yes 10
Fraction 2

Answer 2

This is simplest -- in this format -- using union all:
with t as (
Select MyVar, count(MyVar) as cnt
from MyTable
group by MyVaR
)
select MyVar
from t
union all
select 'Ratio', sum(case when MyVar = 'Yes' then cnt else 0 end) / sum(case when MyVar = 'No' then cnt else 0 end)
from t;
That said, I would just use conditional aggregation and put all values in a single row:
select sum(case when MyVar = 'Yes' then cnt else 0 end) as yes,
sum(case when MyVar = 'Yes' then cnt else 0 end) as no,
sum(case when MyVar = 'Yes' then cnt else 0 end) / sum(case when MyVar = 'No' then cnt else 0 end) as ratio
from t;