COUNT(DISTINCT()) Return false value - sql-server

Question

I try to count total employee in my subquery table. Suppose the count result will return 0, but it keeps returning 1.
If I try to return only employee_id and month together, I didn't get any return value for may which is correct, but each time I try to count(distinct), I will get 1 as my return value. This is my sql
SELECT
count (distinct(CASE WHEN (x.month =5 and x.employee_id <> 0) THEN
x.employee_id
ELSE 0 END)) as test_may
FROM(
(
SELECT
h.month,
h.employee_id,
eb.employee_no,
ee.company_code,
h.amount,
h.year,
h.trx_type,
h.trx_code,
v.trx_desc,
h.frequency,
h.run_sequence
FROM
v_employee h,
v_trans v,
employee_emp ee,
employee eb
WHERE
( h.year = 2014 ) AND
( h.employee_id = ee.employee_id ) AND
( ee.employee_id = eb.employee_id ) AND
( h.employee_no = eb.employee_no ) AND
( h.trx_code = v.trx_code ) AND
( h.trx_type = v.trx_type ) AND
( v.company_code = ee.company_code OR v.company_code is NULL) AND
( h.trx_type IN ('S','B','N','O','A','D','L') )
)
)x,
employee_emp ee,
employee eb
WHERE
( x.employee_id = ee.employee_id ) AND
( ee.employee_id = eb.employee_id ) AND
( x.employee_no = eb.employee_no ) AND
( x.year = 2014 )

Answer 1

The count as you have it now will also count the 0 that is in the ELSE clause of the CASE expression. Even with DISTINCT still one instance of that 0 will be counted.
Remove the ELSE 0 so that you have NULL -- which is not counted:
count (distinct(CASE WHEN x.month =5 and x.employee_id <> 0
THEN x.employee_id
END)) as test_may
Note that with NULLIF you can shorten this expression to:
count (distinct(CASE x.month WHEN 5 THEN NULLIF(x.employee_id, 0) END)) as test_may

Answer 2

Your count will return the same count even in both cases. Because you are giving the value for Count function in both the cases.
Change from
count (distinct(CASE WHEN (x.month =5 and x.employee_id <> 0) THEN
x.employee_id
ELSE 0 END))
To
count (distinct(CASE WHEN (x.month =5 and x.employee_id <> 0) THEN
x.employee_id
ELSE NULL END))
Count will just count the values whether it is 0 or 100 as 1 & skip null values while counting. So in the Else condition NULL will give you correct output.