Final answer:
The COUNT(*) function counts all rows in a table, consisting of both NULL and non-NULL values, providing the total row count. To count only non-NULL values in a specific column, use COUNT(column_name).
Step-by-step explanation:
The COUNT(*) function in SQL is used to count the total number of rows in a table, including those with NULL and non-NULL values. When you use COUNT(*), it does not distinguish between different types of data in the rows; it simply returns the total row count.
However, if you want to count only non-NULL values in a specific column, you would use COUNT(column_name) instead, which excludes NULL values in the count for that particular column.