Sean Lange (2/8/2013)
anthony.green (2/8/2013)
Well you learn something new every day.That was the way I was tought back when I was a young whipper snapper, so I guess it just stuck.
Count is one of those funky aggregates. It counts the number of rows regardless of what column, or even a constant, you use as your count. There has long been a myth that counting * is slower then counting 1 but it just isn't true. I have also heard the myth that count(NullableColumn) will ignore nulls in count, this is also not true.
Further clarification: COUNT(DISTINCT colname) will count the number of distinct nonnull values in the specified column. Perhaps this is where the myth of excluding nulls comes from.