Count Star Vs Count Column

The difference is that COUNT(*) counts all the rows of data, including NULL values, while COUNT(column_name) counts only non-NULL values in the specified column. Let's illustrate this using a table named Users.

userId	firstName	lastName	age	country
1	John	Doe	30	Portugal
2	Jane	Don	31	Belgium
3	Zach	Ridge	30	Norway
4	null	Tom	25	Denmark

If you use COUNT(*), the result will be 4 but if you use COUNT(firstName), it will return 3, omitting the null value.