mysql 查询筛选重复数据sql语句
查询重复数据数量
| 代码如下 | |
| select device_id from device group by device_id having count(device_id) > 1; | |
查询所有重复数据
| 代码如下 | |
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select userid, device_id, create_date from device where device_id in (select device_id from device group by device_id having count(device_id) > 1) order by device_id,create_date desc ; |
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重复一条中create_date 最新的那一条
| 代码如下 | |
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select max(create_date) from device group by device_id having count(device_id)>1; |
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筛选查询
| 代码如下 | |
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select * from device where device_id in (select device_id from device group by device_id having count(device_id) > 1) and create_date not in (select max(create_date) from device group by device_id having count(device_id)>1) order by device_id,create_date desc ; |
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下面再看一些实例吧
表结构如下：
| 代码如下 | |
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mysql> desc test1; +--------------+------------------+------+-----+---------+----------------+ |
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subject和RECEIVER 需要做uniq key,但设计时未做，后面的数据就有很多重复的记录。
1. 查询需要删除的记录，会保留一条记录。
| 代码如下 | |
|
select a.id,a.subject,a.RECEIVER from test1 a left join (select c.subject,c.RECEIVER ,max(c.id) as bid from test1 c where status=0 GROUP BY RECEIVER,SUBJECT having count(1) >1) b on a.id< b.bid where a.subject=b.subject and a.RECEIVER = b.RECEIVER and a.id < b.bid |
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2. 删除重复记录，只保留一条记录。注意，subject,RECEIVER 要索引，否则会很慢的。
| 代码如下 | |
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delete a from test1 a, (select c.subject,c.RECEIVER ,max(c.id) as bid from test1 c where status=0 GROUP BY RECEIVER,SUBJECT having count(1) >1) b where a.subject=b.subject and a.RECEIVER = b.RECEIVER and a.id < b.bid; |
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好了筛选重复数据的sql语句大概就这些了，如果你能理解那几乎不担心重复数据这一说了。
