今天遇到了一个问题，想通过视图将两个表连接起来，其中一个表字段不全，这时候肯定合不到一起，如果加一个冗余字段也不合适，后来发现通过一个sql就可以实现，参考：
SELECT `agent_id` AS `agent_id`, `distributor_id` AS `distributor_id`, `serial_sn` AS `serial_sn`, `e_s_ledger_record`.`order_sn` AS `order_sn`, `create_time` AS `create_time`, `ledger_amount` AS `money`, 1 AS `type` FROM `e_s_ledger_record`
union
SELECT `agent_id` AS `agent_id`, `distributor_id` AS `distributor_id`, `withdraw_sn` AS `serial_sn`, '' AS `order_sn`, `create_time` AS `create_time`, `money` AS `money`, 2 AS `type` FROM `e_s_withdraw`
上边sql是将两个不同业务合到一起的，通过type区分进账出账，由于字段不统一，于是可以通过 “2 AS `type`” 实现，这样最后的表里就会出现这个字段，且全部值都是2啦
