I am able to solve for change of employees between months. Yet find solution on another conditions.

Here is the Parameter created and bind to employees UID.

SELECT

XSA('xxx@abc.com'.'Capacity Reports')."Columns"."Emp UID" s_1
FROM XSA('xxx@abc.com'.'Capacity Reports')
WHERE
(("Columns"."Emp UID" IN
(
SELECT saw_0 FROM (SELECT
"Columns"."Emp UID" saw_0
FROM XSA('xxx@abc.com'.'Capacity Reports')
WHERE
"Columns"."Month" = @parameter("Start")(timestamp'')

) nqw_1
)) AND ("Columns"."Emp UID" NOT IN
(
SELECT saw_0 FROM (SELECT
FROM XSA('xxx@abc.com'.'Capacity Reports')
WHERE
"Columns"."Month" =@parameter("End")(timestamp'')

) nqw_1
)))