SQL: HAVING Clause

The Having clause is optional and used in combination with the Group By clause. It is similar to the Where clause, but the Having clause establishes restrictions that determine which records are displayed after they have been grouped. It is typically placed near the end of the SQL statement, and a SQL statement with the Having clause may or may not include the Group By clause.

The syntax for Having is as follows:

SELECT column1, ... column_n, aggregate_function (expression) 
FROM table_name 
[WHERE condition] 
[GROUP BY column1, ... column_n] 
HAVING condition

Example #1

Select Item, Sum(Price) as TotalSum 
From Antiques 
Group by Item 
Having Sum(Price)>57 

This query returns a list of different items and a field called ‘TotalSum’ that counts the result sum of antiques that supply each item. The Having clause will return only those items with result sum greater than 57 dollars.  

Example #2

Select SellerID, Count(*) as Number_of_Sellers 
From Antiques 
Where BuyerID=21 
Group by SellerID 
Having Count(*)>1 

This example displays a list of seller’s ids, along with their count, but only where there are more than one seller with BuyerID equal to 15.

Example #3

SELECT Item, COUNT(Item) AS Total, MAX(Price) AS MaxPrice 
FROM Antiques 
GROUP BY Item 
HAVING COUNT(Item) > 1 AND MAX(Price) < 500

This example returns a list of items only where the whole group meets the criteria of the Having clause, that is only items of which there are more than 1, and none of which cost more than $500. This is an example of linking multiple expressions together by logical operators such as AND and OR. A Having clause can contain up to 40 such expressions.