mysql的insert into from select 和update by select

从contact表生成dialog表的uid, contact_uid, last_msg_id,
last_msg_time, total_msg_count:
insert into sns_user_00.user_dialog_00(uid,
contact_uid,last_msg_time, last_msg_id, totle_msg_count) select uid,
contact_uid, ctime as last_msg_time, msg_id as last_msg_id, count(*) as
total_msg_count from (select msg_id,
uid, contact_uid, ctime, type from sns_user_00.user_contact_00 order by ctime
desc) `temp` group by uid, contact_uid order
by ctime desc;

上面语句实现了insert into select，其中包括查询每一个类别中时间最晚的记录，利用嵌套select

从contact表生成dialog表的last_recv_time:

insert into
sns_user_00.user_dialog_00(uid, contact_uid, last_recv_time) select * from (
select uid, contact_uid, ctime as recv_time from sns_user_00.user_contact_00
where type=1 order by ctime desc ) `temp`
group by uid,contact_uid order by recv_time desc on duplicate key update last_recv_time =
values(last_recv_time);

上面语句实现了从结果集中去值然后update， 当然如果是多字段的话 last_recv_time = values(last_recv_time)可以写多个，以逗号隔开。

有时候可以利用mysql自身实现数据转移，不必从db导出为文本，然后再处理为新的插入语句，最后再执行一次导入。