mySQL 查詢篩選重複資料sql語句

查詢重複資料數量

代碼如下	複製代碼
select device_id from device group by device_id having count(device_id) > 1;

查詢所有重複資料

代碼如下	複製代碼
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 ;

重複一條中create_date 最新的那一條

代碼如下	複製代碼
select max(create_date) from device group by device_id having count(device_id)>1;

篩選查詢

代碼如下	複製代碼
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 ;

下面再看一些執行個體吧

表結構如下：

代碼如下

複製代碼

mysql> desc test1; +--------------+------------------+------+-----+---------+----------------+ | Field        | Type             | Null | Key | Default | Extra          | +--------------+------------------+------+-----+---------+----------------+ | ID           | int(10) unsigned | NO   | PRI | NULL    | auto_increment | | SENDERNAME   | varchar(32)      | YES  |     | NULL    |                | | RECEIVERNAME | varchar(64)      | YES  |     | NULL    |                | | SENDER       | varchar(64)      | NO   |     | NULL    |                | | RECEIVER     | varchar(64)      | NO   |     | NULL    |                | | SUBJECT      | varchar(512)     | NO   |     | NULL    |                | | CONTENT      | text             | NO   |     | NULL    |                | | PRIORITY     | int(11)          | NO   | MUL | NULL    |                | | STATUS       | int(11)          | NO   | MUL | NULL    |                | | CREATETIME   | datetime         | NO   |     | NULL    |                | | SENDTIME     | datetime         | YES  |     | NULL    |                | +--------------+------------------+------+-----+---------+----------------+

subject和RECEIVER   需要做uniq key,但設計時未做，後面的資料就有很多重複的記錄。

1. 查詢需要刪除的記錄，會保留一條記錄。

代碼如下	複製代碼
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

2. 重複資料刪除記錄，只保留一條記錄。注意，subject,RECEIVER 要索引，否則會很慢的。

代碼如下	複製代碼
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;

好了篩選重複資料的sql語句大概就這些了，如果你能理解那幾乎不擔心重複資料這一說了。