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）以下查詢會報錯誤：[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
應改爲：
select * from test1 where name like 'A%'
union
select * from test1 where name like 'B%' order by name
因爲union中，在不用括號的情況下，只能用一個order by（如果union兩邊的order by的列名不一樣會怎麼樣，通過別名變成一樣再order by）,這會對union後的結果集進行排序
或者改爲：
（select * from test1 where name like 'A%' order by name）
union
（select * from test1 where name like 'B%' order by name）
這兩個order by在union前進行
（2）同樣的limit
（3）UNION和UNION ALL區別
union會過濾掉union兩邊的select得到的結果集中的重複的行，而union all不會過濾掉重複的行
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增量更新的時候，是從另一個表中查詢出來的數據
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());