DQL (Doctrine Query Language) - GROUP BY, HAVING clauses.php

<ul>
<li> GROUP BY and HAVING clauses can be used for dealing with aggregate functions
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<li> Following aggregate functions are availible on DQL: COUNT, MAX, MIN, AVG, SUM
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Selecting alphabetically first user by name.
<div class='sql'>
<pre>
SELECT MIN(u.name) FROM User u
</pre>
</div>

Selecting the sum of all Account amounts.
<div class='sql'>
<pre>
SELECT SUM(a.amount) FROM Account a
</pre>
</div>

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<li> 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.

<div class='sql'>
<pre>
SELECT u.*, COUNT(p.id) FROM User u, u.Phonenumber p GROUP BY u.id
</pre>
</div>

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<li> 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
<div class='sql'>
<pre>
SELECT u.* FROM User u, u.Phonenumber p HAVING COUNT(p.id) >= 2
</pre>
</div>

</ul>