SELECT MIN or MAX from multiple UNION Select Statements

My colleague was trying to select the minimum value from output from multiple Select statements that were joined by a UNION join. This MIN value has to be returned as a column as part of another complex SELECT statement.

Don't know if I explained that well but run the following code and you will understand :)

----- SELECT MIN or MAX from multiple UNION Select Statements
SELECT
ColumnList
, (SELECT
MIN(A)
FROM
(SELECT 4 AS A
UNION
SELECT 2 AS A) AS B
) AS AliasName
FROM
.....