* GROUP BY and HAVING clauses can be used for dealing with aggregate functions * Following aggregate functions are availible on DQL: COUNT, MAX, MIN, AVG, SUM Selecting alphabetically first user by name. <code> SELECT MIN(u.name) FROM User u </code> Selecting the sum of all Account amounts. <code> SELECT SUM(a.amount) FROM Account a </code> * Using an aggregate function in a statement containing no GROUP BY clause, results in grouping on all rows. In the example above we fetch all users and the number of phonenumbers they have. <code> SELECT u.*, COUNT(p.id) FROM User u, u.Phonenumber p GROUP BY u.id </code> * The HAVING clause can be used for narrowing the results using aggregate values. In the following example we fetch all users which have atleast 2 phonenumbers <code> SELECT u.* FROM User u, u.Phonenumber p HAVING COUNT(p.id) >= 2 </code> <code type="php"> // retrieve all users and the phonenumber count for each user $users = $conn->query("SELECT u.*, COUNT(p.id) count FROM User u, u.Phonenumber p GROUP BY u.id"); foreach($users as $user) { print $user->name . ' has ' . $user->Phonenumber[0]->count . ' phonenumbers'; } </code>