Get AVG ignoring Null or Zero values

Question

How can I get the AVG of a column ignoring NULL and zero values?

I have three columns to get their average, I try to use the following script:

SELECT distinct      AVG(cast(ISNULL(a.SecurityW,0) as bigint)) as Average1      ,AVG(cast(ISNULL(a.TransferW,0) as bigint)) as Average2      ,AVG(cast(ISNULL(a.StaffW,0) as bigint)) as Average3 FROM Table1 a,  Table2 b WHERE a.SecurityW <> 0 AND a.SecurityW IS NOT NULL AND a.TransferW<> 0 AND a.TransferWIS NOT NULL AND a.StaffW<> 0 AND a.StaffWIS NOT NULL AND MONTH(a.ActualTime) = 4 AND YEAR(a.ActualTime) = 2013 

I don't get any results, however the three columns have values including NULL and zeros!

Is there anyway to exclude null values before getting the average?

example: AVERAGE(NOTNULL(SecurityW))

Answer 1

NULL is already ignored so you can use NULLIF to turn 0 to NULL. Also you don't need DISTINCT and your WHERE on ActualTime is not sargable.

SELECT AVG(cast(NULLIF(a.SecurityW, 0) AS BIGINT)) AS Average1,        AVG(cast(NULLIF(a.TransferW, 0) AS BIGINT)) AS Average2,        AVG(cast(NULLIF(a.StaffW, 0) AS BIGINT))    AS Average3 FROM   Table1 a WHERE  a.ActualTime >= '20130401'        AND a.ActualTime < '20130501'  

PS I have no idea what Table2 b is in the original query for as there is no join condition for it so have omitted it from my answer.

Answer 2

this should work, haven't tried though. this will exclude zero. NULL is excluded by default

AVG (CASE WHEN SecurityW <> 0 THEN SecurityW ELSE NULL END)