Count(*) Vs Count('column')

Count(*):
1. COUNT(*) returns the number of rows that match the search conditions specified in the query without eliminating duplicates.

 SELECT COUNT(*)
 FROM titles

2.COUNT(*) can be combined with other aggregate functions.

 SELECT COUNT(*), AVG(price)
 FROM titles
 WHERE advance > $1000


 SELECT COUNT(DISTINCT city)
 FROM authors
Remark:

COUNT(*) returns the number of items in a group, including NULL values and duplicates.

COUNT(ALL expression) evaluates expression for each row in a group and returns the number of nonnull values.

COUNT(DISTINCT expression) evaluates expression for each row in a group and returns the number of unique, nonnull values.