Sumarising a table

Question

Using SQL Server I'm trying to summarize a questionnaire table as follows but am struggling!

I want to show the % of all Questionnaires answered true by month and year.

Can anyone help?

Answer 1

You can do this with conditional aggregation. This method shows conditional use of avg():

select "Year", "Month",
       avg(case when recommend = 'true' then 1.0 else 0.0 end) * 100 as "True %"
from Questionnaire q
group by "Year", "Month"
order by "Year", "Month";

If you actually want the "%" at the end, you need to convert the result to a string and append it.