Writing a subquery using Zend DB

Question

Hi

I am having some problems turning the SQL below into a Zend Db query.

$select = ' SELECT s.id, i.id as instance_id, i.reference, i.name, i.sic_code, i.start_date
    FROM sles s
    JOIN sle_instances i
    ON s.id = i.sle_id
    WHERE i.id = ( SELECT MAX(id) 
        FROM sle_instances 
        WHERE sle_id = s.id
        )
    ORDER BY i.name ASC';

I have got as far as the code before - but Zend Db isn't producing the query correctly. Can any one show me what I missing??

$select = $db->select() ->from('sles', array(   'id',
                                                'instance_id'   => 'sle_instances.id',                                                                                          
                                                'reference'     => 'sle_instances.reference',           
                                                'name'          => 'sle_instances.name',
                                                'sic_code'      => 'sle_instances.sic_code',
                                                'start_date'    => 'sle_instances.start_date'
                                             )
                              )
                        ->join('sle_instances', 'sles.id = sle_instances.sle_id')
                        ->where('sles.id = (SELECT MAX(id) FROM sle_instances WHERE sle_id = sles.id)')
                        ->order('sle_instances.name ASC');

The SQL does work by the way. I am rewriting it using Zend Db as I wish to use the Zend Paginator functionality.

Any help is greatly appreciated.

PJ

Answer 1

This:

    $select = $db->select()->from(array("s" => "sles"), array("s.id","i.id as instanceid","i.reference","i.name","i.sic_code","i.start_date"))
                                 ->join(array('i' => "sle_instances"),"s.id = i.sle_id",array())
                                 ->where("i.id = (select max(id) from sle_instances where sle_id = s.id)")
                                 ->order('i.name asc');

Gives this:

"SELECT `s`.`id`, `i`.`id` AS `instanceid`, `i`.`reference`, `i`.`name`, `i`.`sic_code`, `i`.`start_date` FROM `sles` AS `s`
 INNER JOIN `sle_instances` AS `i` ON s.id = i.sle_id WHERE (i.id = (select max(id) from sle_instances where sle_id = s.id)) ORDER BY `i`.`name` asc"

Answer 2

if you want, you can take what @karim79 did and turn your subselect into a $this->select() as well...

$subselect = $db->select()
->from('sle_instances', array(new Zend_Db_Expr('max(id)')))
->where('sle_id = s.id');

$select = $db->select()->from(array("s" => "sles"), 
array("s.id","i.id as instanceid","i.reference","i.name","i.sic_code","i.start_date"))
->join(array('i' => "sle_instances"),"s.id = i.sle_id",array())
->where("i.id = ($subselect)")
->order('i.name asc');

print($select);

//SELECT `s`.`id`, `i`.`id` AS `instanceid`, `i`.`reference`, `i`.`name`, `i`.`sic_code`, `i`.`start_date` FROM `sles` AS `s` INNER JOIN `sle_instances` AS `i` ON s.id = i.sle_id WHERE (i.id = (SELECT max(id) FROM `sle_instances` WHERE (sle_id = s.id))) ORDER BY `i`.`name` asc

Answer 3

Hi, everyone.

I had a very similar problem and I found that this query can be easily written as follows:

$select = $db->select()
  ->from (
    array("s" => "sles"), 
    array(
      "s.id",
      "instanceid" => "i.id",
      "i.reference",
      "i.name",
      "i.sic_code",
      "i.start_date")
  )
  ->join(
    array('i' => "sle_instances"),
    "s.id = i.sle_id",
    array()
  )
  ->where ("i.id = (" . 
    $db->select()
    ->from('sle_instances', array(new Zend_Db_Expr('max(id)')))
    ->where('sle_id = s.id');
  .")")
  ->order('i.name asc');
print($select);

It is exactly the same as people has already stated here. But I felt it is a little easier to read since the sub-query dependencies are more evident.