Cannot use an aggregate or a subquery in an expression used for the group by list of a GROUP BY clause

Question

In the below sql statement i get the following error

Cannot use an aggregate or a subquery in an expression used for the group by list of a GROUP B

Answer 1

You do not need to group by that CASE expression.

SELECT
    T.Post,
    COUNT(*) AS ClientCount,
    CASE COUNT(*) WHEN '1' THEN MIN(T.Client) ELSE '[Clients]' END Client
FROM
    MyTable T
GROUP BY
    T.Post