Adding percentages to multiple counts in one SQL SELECT Query

Question

I have a SELECT statement similar to the one below which returns several counts in one query.

SELECT  invalidCount = (SELECT COUNT(*) FROM <...a...> WHERE <...b...>),
        unknownCount = (SELECT COUNT(*) FROM <...c...> WHERE <...d...>),
        totalCount   = (SELECT COUNT(*) FROM <...e...> WHERE <...f...>)

This works fine but I wanted to add two percentage columns to the SELECT:

invalidCount * 100 / totalCount AS PercentageInvalid, 
unknownCount * 100 / totalCount AS UnknownPercentage

How do I modify my SELECT statement to handle this?

Answer 1

You can use a subquery in the from clause:

select
    s.invalidCount,
    s.unknownCount,
    s.totalCount,
    invalidCount * 100 / s.totalCount as PercentageInvalid,
    unknownCount * 100 / s.totalCount as PercentageUnknown
from
    (select  invalidCount = (SELECT COUNT(*) FROM <...a...> WHERE <...b...>),
        unknownCount = (SELECT COUNT(*) FROM <...c...> WHERE <...d...>),
        totalCount       = (SELECT COUNT(*) FROM <...e...> WHERE <...f...>)) s