collection->addFieldToSelect('col_name') will include the ID column in result. To return only columns of interest, use

$collection->getSelect()
    ->reset(Zend_Db_Select::COLUMNS)
    ->columns(['col_name']);

Example:

$collection->getSelect()
   ->reset(Zend_Db_Select::COLUMNS)
   ->columns(['entity_id' => 'mageproductid', 'value' => 'userid']);
$result = $collection->toArray();

$result output:

 array(2) {
  ["totalRecords"] => int(1565)
  ["items"] => array(1565) {
    [0] => array(2) {
      ["entity_id"]...

Get the last entry of each applicant in history table:

$installer = $this;
$db = $installer->getConnection();

$table  = $installer->getTable('table/name');
$select = $db->select()
    ->from(['t1'=>$table], ['log_id', 'applicant_id', 'grade', 'attendance'])
    ->joinLeft(['t2'=>$table], 't1.applicant_id = t2.applicant_id AND t1.created_at < t2.created_at', [])
    ->where('t2.created_at IS NULL');
$items = $db->fetchAll($select);

If the custom options of a product are the same across stores, but somehow there are not defaulted to store 0, the method below will default all custom options to store 0:

admin > product page > Custom Options > Change to other store > F12 to bring up the dev tools > in console > run

$$('.product-option-scope-checkbox').each(function(e){e.checked=true;})

Or

$$('input[type="checkbox"]').each(function(e) {	e.checked = true; });

Then save. Repeat for other store views.

In DB, the entries in the product option tables ...

<?php if(!Mage::getBlockSingleton('page/html_header')->getIsHomePage()): ?>
    <p class="note-msg"><?php echo $this->__('There are no products matching the selection.') ?></p>
<?php endif ?>

When a block directive, double curly brackets: {{block type="module/block"}} is called in the static block, it is necessary to whitelist the block type in
admin > System > Permissions > Block. Otherwise, it will not render.

Alternatively, the block can be whitelist in the table permission_block directly.

Reference Mage_Core_Model_Email_Template_Filter::blockDirective()

/**
 * Add new radio option 'Moby' to Application Type
 * Affect products: i14, i14u, i14g
 */
$optionTitle = 'Application Type';
$values[] = array(                          
    'title'           => 'Moby',
    'price'           => -750,                         
    'sku'             => 'co_type_mob1',
    'sort_order'      => 50,
    'option_type_id'  => -1, 
    'is_delete'       => 0, 
    'price_type'      => 'fixed'
);
$fields = array(
    'max_characters'    => 0,
    'type'              => 'radio',
    'title'             => $op...

Each uploaded file is processed here:
Mage_Catalog_Model_Product_Option_Type_File::_validateUploadedFile()

To see the uploaded files:

$result['$_FILES'] = $_FILES;   
foreach ($_FILES as $key=>$file) {
   $result[$key] = is_uploaded_file($file['tmp_name']);
}
return  Mage::helper('clog')->_echo($result); 

Exception

exception 'Zend_File_Transfer_Exception' with message 'The file transfer adapter can not find "options_808_file"' in ../lib/Zend/File/Transfer/Adapter/Abstract.php:1503

The exception was due to missing `s...

custom module productcoption
config.xml

<config>
    <modules>
        <Somemod_ProductCoption>
            <version>0.0.1</version>
        </Somemod_ProductCoption>
    </modules>
    <global> 
        <resources>
            <productcoption_setup>
                <setup>
                    <module>Somemod_ProductCoption</module>                    
                </setup>                
            </productcoption_setup>            
        </resources>             
        <blocks>
            <productcoption>
                <...

How to update a column in main table from another table's column. Reference:
Varien_Db_Adapter_Pdo_Mysql::updateFromSeelct()

    /**
     * UPDATE maintable t1
     * JOIN sales_flat_order t2 ON t1.application_id = t2.increment_id
     * SET t1.stud_id = t2.appl_id
     * WHERE t1.student_id IS NULL               
     */         
    public function updateStudId()
    {
        $adapter = $this->_getWriteAdapter();
        $select = $adapter->select()
            ->from($this->getMainTable(), array())
            ->joinLeft(a...

OR

$collection->addFieldToFilter('field_name', 
    [
        ['eq' => 'value1'],
        ['eq' => 'value2']
    ]
);
// same as
$collection->addFieldToFilter('field_name', ['value1', 'value2']);

Filter for X or Y

$collection->addFieldToFilter(
    ['k1' => 'mc_status', 'k2' => 'mc_fail'],
    ['k1' => ['in' => [21, 22]], 'k2' => ['null'=> true]]
);

The above retrieves:

SELECT `main_table`.* 
FROM `some_table` AS `main_table` 
WHERE ((mc_status IN(21, 22)) OR (mc_fail IS NULL))

NULL, NOT NULL

...

A sample of different options to add field in Mage_Adminhtml_Block_Widget_Form

Ref Varien_Data_Form_Element_Abstract lib\Varien\Data\Form\Element\Abstract.php

Add Suffix to Element Names

$form = new Varien_Data_Form(['field_name_suffix' => 'ihe']);

Date and Date-time Fields

$dateFormatIso = Mage::app()->getLocale()->getDateFormat(
    Mage_Core_Model_Locale::FORMAT_TYPE_SHORT
);        
$fieldset->addField('established_at', 'date', [
    'name'      => 'established_at',
    'image'     => $this->getSkinUrl('i...

json response

    public function completeAction()
    {
        $orderId = $this->getRequest()->getParam('order_id', false);
        $info['order_id'] = 0;
        if ($orderId) {
          $order = Mage::getModel('patron/order')->load($orderId);
          if ($info['order_id'] = $order->getId()) {
              $info['ostatus'] = $order->getOstatus();
              $info['lat'] = $order->getDeliveredLat();
              $info['lng'] = $order->getDeliveredLng();
          }
        }        
        $this->getResponse()->setHeader(...

Column Types

Take a look at Mage_Adminhtml_Block_Widget_Grid_Column::_getRendererByType() to dive into the different column types:

app\code\core\Mage\Adminhtml\Block\Widget\Grid\Column\Renderer\Abstract.php

1. date
2. datetime
3. number
4. currency
5. price
6. country
7. concat
8. action
9. options
10. checkbox
11. massaction
12. radio
13. input
14. select
15. text
16. store
17. wrapline
18. theme

Code Snippets

Checkbox

See app\code\core\Mage\Adminhtml\Block\Widget\Grid\Column\Renderer\Checkbox.php.

    protected function _p...

base_currency_code
Base currency is used for all online payment transactions. Scope is defined by the catalog price scope ("Catalog" > "Price" > "Catalog Price Scope").

global_currency_code
The default currency configured in the admin, Default Display Currency

order_currency_code
The currency with which order is placed.

store_currency_code
Deprecated, same as base.

base_to_global_rate
Convert from base to global

base_to_order_rate
Convert from base to order, ratio of grand_total and base_grand_total

Load Store by Store Code

$store = Mage::getModel('core/store')->load('store_code');
// or
$store = Mage::app()->getStore('store_code');

Get Store URL

$store->getBaseUrl();

Get Store Secure URL

$store->getBaseUrl(Mage_Core_Model_Store::URL_TYPE_LINK, true);

UPDATE `sales_flat_order` SET
`base_discount_refunded`=null,
`base_shipping_refunded`=null,
`base_shipping_tax_refunded`=null,
`base_subtotal_refunded`=null,
`base_tax_refunded`=null,
`base_total_offline_refunded`=null,
`base_total_online_refunded`=null,
`base_total_refunded`=null,
`discount_refunded`=null,
`shipping_refunded`=null,
`shipping_tax_refunded`=null,
`subtotal_refunded`=null,
`tax_refunded`=null,
`total_offline_refunded`=null,
`total_online_refunded`=null,
`total_refunded`=null,
`hidden_tax_refunded`=null,
`base_hidden_tax_re...

The error is coming from Mage_Catalog_Model_Product_Option_Type_File but it is not interpreted in _getValidatorErrors(). The error happens repeatedly for certain users and not other users.

In $fileInfo = $upload->getFileInfo($file);, the error is 7. For example:

Array
(
    [name] => YU XIA.jpg
    [type] => 
    [tmp_name] => 
    [error] => 7
    [size] => 
    [options] => Array
        (
            [ignoreNoFile] => 
            [useByteString] => 1
            [magicFile] => 
            [detectInfos] => 1
        )

    [...

    /**
     * Resize image recursively until it is less than 25KB and saved as tmp.jpg
     * Original image is unchanged     
     * 
     * @param string fullpath and filename
     * @return string fullpath tmp.jpg that is saved              
     */             
    protected function _resizeImage($fnm)
    {
        if (filesize($fnm) > 25600) {
          $image = new Varien_Image($fnm);
          $image->constrainOnly(false);         
          $image->keepAspectRatio(true);
          $newW = (int) $image->getOriginalWidth() * ...

condA AND (cond1 OR cond2 OR cond3)

$cincId = $session->getCustomerId();
$attributes = array( 
    array('attribute'=>'mc_by', 'eq'=>$clinicId), 
    array('attribute'=>'mc_lb_by', 'eq'=>$clinicId),
    array('attribute'=>'mc_xy_by','eq'=>$clinicId), 
);               
$students = Mage::getResourceModel('moe/stut_collection')
    ->addAttributeToSelect(array('fullname', 'travel_doc_no', 'mc_status'))
    ->addAttributeToFilter($attributes, null, 'left')
    ->setOrder('created_at', 'desc')
;

Short Array:

  ...