Magneto database CRUD

In magento a model is required to perform SQL query in your database tables.
Sort data:

       $collection = Mage::getModel('module/model_name')->getCollection()
       ->addAttributeToSort('order', 'ASC')
        ->addAttributeToSort('last_name', 'ASC')
        ->addAttributeToSort('first_name', 'ASC');

Or Condition:

// Add OR condition:
$collection->addAttributeToFilter(array(
    array(
        'attribute' => 'field_name',
        'in'        => array(1, 2, 3),
        ),
    array(
        'attribute' => 'date_field',
        'from'      => '2000-09-10',
        ),
    ));

$filter_a = array('like'=>'a%');
$filter_b = array('like'=>'b%');
Mage::getModel('catalog/product')
 ->getCollection()
 ->addFieldToFilter('sku', array($filter_a, $filter_b))
 ->getSelect();

Equal:

 
$collection->addAttributeToFilter('field_name', 1);

Where:

$collection->addAttributeToFilter('field_name', array(
    'in' => array(1, 2, 3),
    ));
 
$collection->addAttributeToFilter('date_field', array(
   'from' => '2000-09-10',
    ));
 
$collection->addAttributeToFilter('date_field', array(
    'from' => '10 September 2000',
    'to' => '11 September 2000',
    'date' => true, // specifies conversion of comparison values
    ));
$collection->addAttributeToFilter('field_name', array(
    'notnull' => true,
    ));

Update data:

$collection->setColumnname('value');
$collection->save();

Many more here:
https://www.magentocommerce.com/wiki/1_-_installation_and_configuration/using_collections_in_magento
and here
https://www.magentocommerce.com/knowledge-base/entry/magento-for-dev-part-8-varien-data-collections

Want direct SQL query ???

  
    /**
     * Get the resource model
     */
    $resource = Mage::getSingleton('core/resource');
     
    /**
     * Retrieve the read connection
     */
    $readConnection = $resource->getConnection('core_read');
     
    $query = 'SELECT * FROM ' . $resource->getTableName('catalog/product');
     
    /**
     * Execute the query and store the results in $results
     */
    $results = $readConnection->fetchAll($query);
     
    /**
     * Print out the results
     */
     var_dump($results);