SQL Server 2019

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create table testTable (Column1	varchar(50), Column2 int);
insert into testTable values('A',	200);
insert into testTable values('A',	200);
insert into testTable values('A',	0);
insert into testTable values('B',	300);
insert into testTable values('B',	200);
insert into testTable values('C',	100);
insert into testTable values('D',	0);
7 rows affected

SELECT Column1,
       SUM(Column2) / COUNT(*) AS Column2
FROM testTable where column2<>0
GROUP BY Column1;


Column1
Column2


A
200

B
250

C
100


SELECT Column1,
       Coalesce(SUM(Column2) / nullif(COUNT(CASE WHEN Column2 <> 0 THEN 1 END),0),0) AS Column2
FROM testTable
GROUP BY Column1;


Column1
Column2


A
200

B
250

C
100

D
0


Warning: Null value is eliminated by an aggregate or other SET operation.