SELECT number of groups resulted from a GROUP BY query

Question

I tried the following query to select the number of groups resulting from a GROUP BY query:

SELECT count(*)
FROM (
        SELECT count(*)
        FROM MyTable
        WHERE Col2 = 'x'
        GROUP BY Col1
     )

Unfortunately, this query is not valid: Incorrect syntax near ')'..

Note: I want to get exactly one row (I already found a solution with n times the result, where n = the group count).

Answer 1

SELECT count(*)
FROM (
        SELECT 1 as dummy
        FROM MyTable
        WHERE Col2 = 'x'
        GROUP BY Col1
     ) dt

No need to count rows in the sub-query, the result will be the same anyway.