CREATE TABLE `test1` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`name` varchar(20) NOT NULL,
`desc` varchar(100) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
（1）以下查询会报错误：[Err] 1221 - Incorrect usage of UNION and ORDER BY
select * from test1 where name like 'A%' order by name
union
select * from test1 where name like 'B%' order by name
应改为：
select * from test1 where name like 'A%'
union
select * from test1 where name like 'B%' order by name
因为union中，在不用括号的情况下，只能用一个order by（如果union两边的order by的列名不一样会怎么样，通过别名变成一样再order by）,这会对union后的结果集进行排序
或者改为：
（select * from test1 where name like 'A%' order by name）
union
（select * from test1 where name like 'B%' order by name）
这两个order by在union前进行
（2）同样的limit
（3）UNION和UNION ALL区别
union会过滤掉union两边的select得到的结果集中的重复的行，而union all不会过滤掉重复的行
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增量更新的时候，是从另一个表中查询出来的数据
INSERT INTO order_stay_time(order_id, aging_time, stay_time)
SELECT o.id, TIMESTAMPDIFF(SECOND, o.create_time, NOW()) , TIMESTAMPDIFF(SECOND, order_status_table.create_at, NOW())
FROM `order` o
LEFT JOIN (SELECT order_id, MAX(create_at) AS create_at FROM order_track_log GROUP BY order_id) AS order_status_table
ON order_status_table.order_id = o.id
WHERE o.order_status not in ("Completed","Cancel","RTO","ReturnDelivered","Expired")
ON DUPLICATE KEY UPDATE
aging_time=TIMESTAMPDIFF(SECOND, o.create_time, NOW()),
stay_time=TIMESTAMPDIFF(SECOND, order_status_table.create_at, NOW());