[SOLVED] Zend_Db_Select: LEFT JOIN on a subselect

Zend_Db_Select: LEFT JOIN on a subselect

I have a query, that does a LEFT JOIN on a subselect. This query is run in a high load environment and performs within the set requirements. The query (highly simplified) looks like:

SELECT
  table_A.pKey
, table_A.uKey
, table_A.aaa
, table_B.bbb
, alias_C.ccc
, alias_C.ddd
FROM table_A
INNER JOIN table_B ON table_A.pKey = table_B.pKey
LEFT JOIN (

    SELECT
      table_X.pKey
    , table_X.ccc
    , table_Y.ddd
    FROM table_X
    INNER JOIN table_Y ON table_X.pKey = table_Y.pKey

  ) AS alias_C ON table_A.uKey = alias_C.pKey;

^{(for various reasons, it is not possible to rewrite the subselect as a (direct) LEFT JOIN).}

Now, I cannot get the LEFT JOIN on subselect to work with Zend_Db_Select. I've tried everything I could come up with, but it does not work.

So my question is:

Is it not possible to do a query as described above with Zend_Db_Select?
What syntax do I need to get it to work within Zend Framework?

Solution

I think that it should work like this:

$subselect = $db->select->from(array('x' => 'table_X'), array('x.pKey', 'x.ccc', 'y.ddd'), 'dbname')
                        ->join(array('Y' => 'table_Y'), 'x.pkey = y.pkey', array(), 'dbname');

$select = $db->select->from(array('a' => 'table_A'), array(/*needed columns*/), 'dbname')
                     ->join(array('b' => 'table_B'), 'a.pkey = b.pkey', array(), 'dbname')
                     ->joinLeft(array('c' => new Zend_Db_Expr('('.$subselect.')'), 'c.pkey = a.ukey', array())

I haven't tried it but I believe it'll work.