views里面添加 表达式 expression
https://www.drupal.org/docs/7/api/database-api/dynamic-queries/expressions
select max 最大值
https://blog.csdn.net/xx_star1204/article/details/88187631
https://www.drupal.org/forum/support/module-development-and-code-questions/2009-03-22/implementing-custom-sql-query-for
$sub_query = db_select('workflow_node_history', 'sub_workflow_node_history_states');
$sub_query->addField('sub_workflow_node_history_states', 'nid');
$sub_query->addField('sub_workflow_states', 'weight', 'weight');
$sub_query->addField('sub_workflow_states_old', 'weight' , 'old_weight');
$sub_query->addJoin('LEFT', 'workflow_states', 'sub_workflow_states', 'sub_workflow_node_history_states.sid = sub_workflow_states.sid');
$sub_query->addJoin('LEFT', 'workflow_states', 'sub_workflow_states_old', 'sub_workflow_node_history_states.old_sid = sub_workflow_states_old.sid');
$sub_query->orderBy('sub_workflow_node_history_states.hid', 'DESC');
$join = new views_join();
$join->definition = array('table formula' => $sub_query, 'left_field' => 'nid', 'field' => 'nid', 'left_table' => 'node');
$join->left_table = 'node';