COUNT function provides a count of the rows in a result set. It has two forms. COUNT(*) counts rows regardless of data values in the rows, while COUNT(column_name) counts only non-null values in the named colum

the DBMS assigns a column name for the result based on its own internal rules. You can always provide your own column name by assigning an alias right after the expression that forms the column

As in mathematics, an SQL function returns a single value each time it is executed