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.
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:
SELECT DeptID, SUM(SaleAmount) FROM Sales WHERE SaleDate = '01-Jan-2000' GROUP BY DeptID HAVING SUM(SaleAmount) > 1000
Referring to the sample tables in the Join example, the following query will return the list of departments which have more than 1 employee:
SELECT DepartmentName, COUNT(*) FROM Employee, Department WHERE Employee.DepartmentID = Department.DepartmentID GROUP BY DepartmentName HAVING COUNT(*)>1;
HAVING is convenient, but not necessary. Code equivalent to the example above, but without using
HAVING, might look like:
SELECT * FROM ( SELECT DepartmentName AS deptNam, COUNT(*) AS empCnt FROM Employee AS emp, Department AS dept WHERE emp.DepartmentID = dept.DepartmentID GROUP BY deptNam ) AS grp WHERE grp.empCnt > 1;
- "SQL HAVING Clause". w3schools.com.
The HAVING clause was added to SQL because the WHERE keyword could not be used with aggregate functions.