PHP

 

Difference between a "where" clause and a "having" clause? 

Though the HAVING clause specifies a condition that is similar to the purpose of a WHERE clause, the two clauses are not interchangeable. Listed below are some differences to help distinguish between the two:

1. The WHERE clause specifies the criteria which individual records must meet to be selcted by a query. It can be used without the GROUP BY clause. The HAVING clause cannot be used without the GROUP BY clause.
2. The WHERE clause selects rows before grouping. The HAVING clause selects rows after grouping.
3. The WHERE clause cannot contain aggregate functions. The HAVING clause can contain aggregate functions.