摘要：
use DB; -- 添加索引，index_type为索引名称，student为表名 type为列表 ALTER TABLE `student` ADD INDEX index_type (`type`) -- 删除索引，index_type为索引名称，student为表名 drop index i 阅读全文
摘要：
(from b in _db.order_info where b.status != 3 group new { b.batchnumber, b.create_time } by new { b.merchant_id, b.batchnumber } into g select new Use 阅读全文