Sub Query

To use a sub query like table, pass it as argument (instead of the name of the table). You will get in return an instance of SubQueryTable that you can use like normal table (eg. you can set alias).

$qb = $phuriaSQL->createSelect();
$subQb->addSelect('MAX(pricelist.price) AS price');
$subQb->from('pricelist');
$subQb->addGroupBy('pricelist.owner_id');

$qb = $phuriaSQL->createSelect();
$subTable = $qb->from($subQb, 'src');
$qb->addSelect("AVG({$subTable->column('price')})");

echo $qb->buildSQL();

SELECT AVG(src.price) FROM (SELECT MAX(pricelist.price) AS price
FROM pricelist GROUP BY pricelist.owner_id) AS src

If you want to use sub query in a different context then you must use object to string reference converter.

$qb = $phuriaSQL->createSelect();
$subQb->addSelect('DISTINCT user.affiliate_id');
$subQb->form('user');

$qb = $phuriaSQL->createSelect();
$qb->addSelect("10 = ({$qb->objectToString($subQb)})");

echo $qb->buildSQL();

SELECT 10 IN (SELECT DISTINCT user.affiliate_id FROM user)

At the time of building query ReferenceParser will be known what to do with it.