Get AVG ignoring Null or Zero values

问题:

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))

回答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.

回答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)

回答3:

In Case of not considering '0' or 'NULL' in average function. Simply use

AVG(NULLIF(your_column_name,0))

回答4:

worked for me：

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

回答5:

You already attempt to filter out NULL values with NOT NULL. I have changed this to IS NOT NULL in the WHERE clause so it will execute. We can refactor this by removing the ISNULL function in the AVG method. Also, I doubt you'll actually need bigint so we can remove the cast.

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