The WHERE clause selects rows before grouping. The HAVING clause selects rows after grouping.
The WHERE clause cannot contain aggregate functions. The HAVING clause can contain aggregate functions.

A HAVING clause is like a WHERE clause, but applies only to groups as a whole, whereas the WHERE clause applies to individual rows. A query can contain both a WHERE clause and a HAVING clause. The WHERE clause is applied first to the individual rows in the tables . Only the rows that meet the conditions in the WHERE clause are grouped. The HAVING clause is then applied to the rows in the result set.