custom query in magento

Database connection in magento
<?php  

   // Get the resource model
    $resource = Mage::getSingleton('core/resource');
   
    // Retrieve the read connection

    $readConnection = $resource->getConnection('core_read');
   
     // Retrieve the write connection

    $writeConnection = $resource->getConnection('core_write');

     //get table name

    $tableName = $resource->getTableName('catalog_product_entity');

 // or get table name from an entity name



    $tableName = $resource->getTableName('catalog/product');

read select query in magento (read data from select query)

    $query = 'SELECT * FROM ' . $resource->getTableName('catalog/product');
    
    // Execute the query and store the results in $results
    $results = $readConnection->fetchAll($query);
    
  // Print out the results
    print_r($results);

read only one column from select query in magento (read data from select query)

 $name= $readConnection->fetchCol('SELECT name FROM ' . $tableName . ');

 print_r($name);


read only one cell or fetchone item attribute value from product table
  $productId = 101;
  $query = 'SELECT name FROM ' . $tableName . ' WHERE entity_id = '. $productId . ' LIMIT 1';
  $name = $readConnection->fetchOne($query);
  echo $name;


 update query in magento
   $newSku = 'new-sku';
   $updateQuery = "UPDATE {$tableName} SET sku = '{$sku}' WHERE entity_id = ".$productId;
   $writeConnection->query($updateQuery );


?>