Having (SQL)
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.
Having clause filters the data on the group row but not on the individual row.
To view the condition present in group formed by GROUP BY clause,HAVING clause is used.
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:
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;