revision in drupal

db_query('DELETE FROM {node_revisions} nr WHERE nr.vid NOT IN (SELECT n.vid FROM {node} n)');

You don't want to delete all the revisions: You want to delete all but the current revision.

在content-type-form里面有个选项create a new revision 如果选择了这个 则每次修改node的时候 都会生成一个新的node revision

也有这样的选择

function YOUR_MODULE_form_alter(&$form, &$form_state, $form_id) {
    //drupal_set_message("Form ID is : " . $form_id);
    switch($form_id) {
        case 'CONTENT_TYPE_node_form':
            //dpm($form);
            $form['actions']['submit']['#submit'][] = 'revision_control_node_form_submit';
            $form['actions']['submit']['#submit'] = array_reverse($form['actions']['submit']['#submit']); // reverse array to put our submit handler first
            break;
    }

}

function revision_control_node_form_submit($form, &$form_state) {
    if($form_state['values']['your_taxonomy_field'] == 'your_value') {
        $form_state->revision = 1;
    }
}

http://stackoverflow.com/questions/21451567/how-to-enable-disable-revision-in-drupal-7