My Co-worker complained me that AVG function is not properly working in SQL Server whereas it works correctly in mysql. I immediately told him that AVG does the implicit convertion by default and the result may be wrong (based on datatype).

Consider the following set of data

select avg(col) from
(
	select 1 as col union all
	select 2
) as t

average
-----------
1

select avg(col*1.0) as average,avg(cast(col as decimal(12,2))) as average from
(
	select 1 as col union all
	select 2
) as t

average                                 average
--------------------------------------- ---------------------------------------
1.500000                                1.500000