Yii2.0中使用Union查询，并使用join，支持分页

 1 $query1 = Class1::find()->where($where);
 2 $query2 = Class1::find()->alias('a')->join('left join', Class2::tableName() . 'as b', 'b.id = a.objId')
　　　　　　　　->select('a.*')->where($where2);
 3 $queryAll = $query1->union($query2, true);
 4 $query = (new Query())->from(['c' => $queryAll])->select('c.*,d.type,d.title')
　　　　　　　　->join('left join', Class3::tableName() . 'as d', 'd.id = c.objId')->distinct(true)->orderBy(['c.time'=>SORT_DESC]);
 5 $sql = $query->createCommand()->getRawSql();
 6 $result = $query->offset(($page - 1) * 10)->limit(10)->all();
 7 
 8 $totalCount = $query->count();
 9 $pagination = new Pagination(['totalCount'=>$totalCount, 'pageSize'=>10]);
10 $result = $query->offset($pagination->offset)->limit($pagination->limit)->all();