If you're converting over to ZF1 from ZF2, there's quite a few subtleties to bridge.  Most of the docs are pretty clear, but I found some aspects of Zend_Db's successor to be a bit more obscure.  Zend_Db was a good friend, especially when came time to adopt query abstraction without going through table gateways.  It was so easy (probably sounding little spoiled now) to do then what I wanted to do now, which is wire a connection outside of Doctrine, in order to connect to an AWS Redshift Cluster (which is awesome by the way) to execute straight queries.

What I Used To Do, That I Wanted Anew

$DB = Zend_Db::factory
(
    'Pdo_Mysql',
    array(
        'host' => 'host',
        'password' => $this->getDatabasePass(),
        'username' => $this->getDatabaseUser(),
        'dbname' => $this->getDatabaseName(),
        'options' => array(
            Zend_Db::AUTO_QUOTE_IDENTIFIERS
        )
    )
);

$S = $DB->select()->from( 'table', array( 'col1', 'col3' ) )
        ->where( 'col2=?', "O'Smith" )
            ->limit( 1 );
$R = $DB->fetchAll( $S );

You'll see below that things have taken a bit of a turn for the more complex. Reading the rationale in all the PRs on GitHub is a bit of a brain-bender, and when you use something like Doctrine for most of the day to day, this is probably a fringe-case thing.

 

Prepping The New Mistress (ZF2)

I first recommend that you wire your connection the ZF2 way.  I've got Doctrine2 already setup in my autoload configuration file -- just need to add a few lines for configuration's sake.

config/autoload/database.local.php

<?php

return array(
    'doctrine' => array(
        'connection' => array(
            'orm_default' => array(
                'driverClass' => 'Doctrine\DBAL\Driver\PDOMySql\Driver',
                'params' => array(
                    'host'         => 'host',
                    'port'         => '3306',
                    'user'         => 'user',
                    'password'     => 'pass',
                    'dbname'       => 'doctrine_mysql_db',                
                )
            )
        )
    ),
    'redshift' => array(
        'connection' => array(
            'stats_default' => array( 
                'driver' => 'Pdo_Pgsql',
                'host' => 'host',
                'dbname' => 'analytics',
                'username' => 'redshift_user',
                'password' => 'redshift_pass',
                'port' => 5439,  
                'charset' => 'UTF8'              
            ),
        ),
    ),
);
You'll notice that I'm using Pgsql above, you may want to change if you're going to use MySQL for example - just need to change the driver string

This done, edit your Module config at the getServiceConfig() level to include a factory to dispatch the connection:

module/Application/Module.php

public function getServiceConfig() 
{
    return array(
        'factories' => array(
            // it's this part that matters
            'redshift_stats' => function ($sm) {
                $config    = $sm->get('config');
                    
                $dbc     = $config['redshift']['connection']['stats_default'];
                $adapter = new \Zend\Db\Adapter\Adapter( $dbc );
                return new \Zend\Db\Sql\Sql( $adapter );
            },
            // end, part that matters
        ),
    );
}

(your mileage may vary) 

Thusly is born the part that lets you do what's below, which is the equivalent to the first (I thought succinct!) ZF1 block we started with: 

$SQL  = $this->getServiceLocator()->get('redshift_stats');
$DBA  = $SQL->getAdapter();
$S    = $SQL->select()
            ->from( 'table' )
            ->columns( array( 'col1', 'col3' ) )  
            ->where( array( "col2" => "O'Smith" ) )
            ->limit( 1 );
            
$sel_string   = $SQL->getSqlStringForSqlObject($S);
$R            = $DBA->query( $sel_string, $DBA::QUERY_MODE_EXECUTE );

Oh yea, fetchAll, fetchOne, and fetchPairs are all gone...  (I ran across a bridge on GitHub someone wrote to try to bridge this extricated functionality).

 

Insertion Queries

Inserts and updates work a bit differently with ZF2 as well.  The ZF1 insert and update would execute right away, you have to extract the string and execute it now.  This can be a gotcha as you get started

With Zend Framework 1

$DB = /* get your connection */;
$DB->insert( 'table', array( 'col1' => 123 ) );

With Zend Framework 2

$DB       = $this->getServiceLocator()->get('redshift_stats'); 
$ADAPTER  = $SQL->getAdapter();
$I        = $SQL->insert( 'table' );

$I->values( array( 'col1' => 123 ) );

$ins_string = $SQL->getSqlStringForSqlObject($I);
$results    = $ADAPTER->query( $ins_string, $ADAPTER::QUERY_MODE_EXECUTE );

Concluding, I hope this helps you bridge the gap between the two.  By no means thorough, I just wanted to highlight the close-but-not-quite elements that would helped me get kickstarted.

The verbosity of it all, and Zend\Db's lack of support for batch inserts (yes I prefer MySQL) really makes adopting the likes of Doctrine2 worthwhile (I find the Mappers turn out cleaner overall).  I think this may have been the MO with ZF2, less ORM, more query abstraction -- please use something else like Doctrine2 for heavy -- scratch that -- usual lifting.