A HAVING clause in SQL specifies that an SQL SELECT statement should only return rows where aggregate values meet the specified conditions. It was added to the SQL language because the WHERE keyword could not be used with aggregate functions.
Examples
To return a list of department IDs whose total sales exceeded $1000 on the date of January 1, 2000, along with the sum of their sales on that date:
Referring to the sample tables in the Join example, the following query will return the list of departments which have more than 1 employee:
HAVING is convenient, but not necessary. Code equivalent to the example above, but without using HAVING, might look like:
References
Having (SQL) Wikipedia(Text) CC BY-SA