Select, where column = alias

Question

Hi,
is it possible to use c.LgDatM in where clause?
I would like to tell him to give me values only for months from column LgDatM.
My where clause:
WHERE MONTH(LogDate) BETWEEN 3 and 4)
and the code
SELECT c.LgDatM, a.EmpCount, b.LgDat FROM
(SELECT MONTH(LogDate) as LgDatM FROM [Prometheus].[dbo].[tblMain])c,
(SELECT COUNT(DISTINCT Enumber) as EmpCount FROM [Prometheus].[dbo].[tblMain]
WHERE MONTH(LogDate) BETWEEN 3 and 4)a,
(SELECT COUNT(DISTINCT LogDate) as LgDat FROM [Prometheus].[dbo].[tblMain]
WHERE MONTH(LogDate) BETWEEN 3 and 4)b
GROUP BY c.LgDatM, a.EmpCount, B.LgDat
GO
Then you very much
Mathh

Answer 1

SELECT Month(logdate)      AS lgdatm, 
       Count(DISTINCT CASE 
                        WHEN Month(logdate) BETWEEN 3 AND 4 THEN enumber 
                        ELSE NULL 
                      END) AS EmpCount, 
       Count(DISTINCT CASE 
                        WHEN Month(logdate) BETWEEN 3 AND 4 THEN logdate 
                        ELSE NULL 
                      END) lgdat 
FROM   [tblmain] 
GROUP  BY Month(logdate)