Multiple cases based on Columns In SQL Query

Question

There is a SQL query given below, that query performs DateDIff operation by selecting max and min date according to
TCard OR you can say id,
here' the query
SELECT
--COUNT(DIFF)
Count(DATEDIFF(D, MinDate, MaxDate)/30) AS DIFF
FROM (
SELECT
   MAX(TDate) AS MaxDate,
   MIN(TDate) AS MinDate
   FROM EDATA
   GROUP BY TCard
)a
Group by DATEDIFF(D, MinDate, MaxDate)/30
Now i want to apply some kind of sorting in this query before performing DateDiff operation (sorting can be based on several parameters
like age, name etc. but 1 at a time according to the cases) 
Now I want to know How to apply cases over this query and where?

Answer 1

You can apply sorting based on certain condition however you need to include those columns in your subquery. On custom sorting check out this article
here:
e.g.
SELECT CountryName
FROM   dbo.Country
ORDER BY CASE WHEN
CountryName = 'INDIA' THEN '1'
WHEN CountryName = 'CHINA' THEN
'2'
ELSE CountryName END ASC
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