NSString*sql=[NSStringstringWithFormat:@"SELECT * FROM chatinfo where (msg_fromId =? and msg_toId = ?) or (msg_fromId =? and msg_toId = ?) order by send_time desc limit ?,?"];
NSString*sql=[NSStringstringWithFormat:@"SELECT * FROM chatinfo where (msg_fromId =? and msg_toId = ?) or (msg_fromId =? and msg_toId = ?) order by msg_seq desc limit ?,?"];