Compare 2 fields in Drupal

I want to do a simple SQL query in Drupal, but I'm not sure how. I would like to achieve this:

SELECT COUNT(nid) AS i_count FROM node WHERE `created` != `changed`;

I have the following code, which doesn't work:

$query = db_select('node', 'n');
$query->addExpression("COUNT(nid)","i_count");
$开发者_如何学运维query->condition("created","changed","!=");
$i_number_published = $query->execute()->fetchCol();

The reason why it doesn't work is that it compares the column created with the string value "changed". Is there any way I can tell it to compare columns instead of column-string?

Use the where() member function to add conditions based on other fields in the table:

$query = db_select('node', 'n');
$query->addExpression("COUNT(nid)","i_count");
$query->where("created != changed");
$i_number_published = $query->execute()->fetchCol();

$result_handler = db_query("select count(nid) from {node} where `created` != `changed`") ; 

$result_arr = db_fetch_array($result_handler) ; 

$number_of_nodes = $result_arr['count(nid)'] ;