Load just one field from node I have x nodes with field named "thefield". My script is checking "thefield" and if he does so the right value is updated. 

How can i get from node just one field for check and didnt load full entity (node_load)?
I would use a db_query to find all nodes that that field appears on and then update them with a node_load here is the code:

$result = db_query('SELECT f.entity_id FROM {field_data_field_thefield} f');
foreach ($result as $record) {
    $node = node_load($record-&gt;entity_id);
    // update node
}