COUNT() in SQL Server

Some considerable point about COUNT() in SQL Server :-

• It comes under aggregate function.
• It returns number of item in group.
• The return type of COUNT() is "INT".
• COUNT(*) returns the number of values in a group, doesn't matter values includes "NULL" or duplicates.
• COUNT(<ColumnName>) returns the number of nonnull values.
• COUNT(DISTINCT <ColumnName>) returns the number of unique, non-null values.

Lets have an example :-