Difference between count(column) and count(*)
count(*) would return an extra row in the result that contains a null and the count of null values in the column.
for eg.
create table #demo(id int,id2 int)
insert #demo values(null,null)
insert #demo values(1,null)
insert #demo values(null,1)
insert #demo values(1,null)
insert #demo values(null,1)
insert #demo values(1,null)
insert #demo values(null,null)
select count(*),count(id),count(id2) from #demo
results 7 3 2
Another minor difference, between using * and a specific column, is that in the column case you can add the keyword DISTINCT, and restrict the count to distinct values
