Question

可能重复：
How can I find duplicate entries and delete the oldest ones in SQL?

由于更新工具错误，我有一个数千个重复的数据库。我能够识别具有重复项的项集合，但是只需删除最旧的条目，不一定是最低的id。测试数据看起来像这样，正确的行有一个*

除了最近创建的行之外，应删除具有重复标题但没有重复规则的文章。（实际的id列是一个GUID所以我不能假设自动递增）

Id           Article id          Rule Id         Title          Opened Date
--           ----------          -------         -----          -----------
1*           111                 5               T1             2013-01-20
2            112                 5               T1             2013-07-01
3*           113                 6               T2             2013-07-01
4*           114                 7               T2             2013-07-02
5            115                 8               T3             2012-07-01
6            116                 8               T3             2013-01-20
7*           117                 8               T3             2013-01-21

表架构：

CREATE TABLE [dbo].[test_ai](
    [id] [int] NOT NULL,
    [ArticleId] [varchar](50) NOT NULL,
    [ruleid] [varchar](50) NULL,
    [Title] [nvarchar](max) NULL,
    [AuditData_WhenCreated] [datetime] NULL,
PRIMARY KEY CLUSTERED 
(
    [id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON)
)

测试数据插页

insert into test_ai (id, articleid, ruleid, title, auditdata_whencreated) values (1, 111, 5, 'test 1', '2013-01-20')
insert into test_ai (id, articleid, ruleid, title, auditdata_whencreated) values (2, 112, 5, 'test 1', '2012-07-01')
insert into test_ai (id, articleid, ruleid, title, auditdata_whencreated) values (3, 113, 6, 'test 2', '2012-07-01')
insert into test_ai (id, articleid, ruleid, title, auditdata_whencreated) values (4, 114, 7, 'test 2', '2012-07-02')
insert into test_ai (id, articleid, ruleid, title, auditdata_whencreated) values (5, 115, 8, 'test 3', '2012-07-01')
insert into test_ai (id, articleid, ruleid, title, auditdata_whencreated) values (6, 116, 8, 'test 3', '2013-01-20')
insert into test_ai (id, articleid, ruleid, title, auditdata_whencreated) values (7, 117, 8, 'test 3', '2013-01-21')

我当前的查询如下所示

select * from test_ai
where test_ai.id in

-- set 1 - all rows with duplicates
(select f.id 
from test_ai as F 
WHERE exists (select ruleid, title, count(id)   
FROM test_ai
    WHERE test_ai.title = F.title
        AND test_ai.ruleid = F.ruleid
    GROUP BY test_ai.title, test_ai.ruleid
    having count(test_ai.id) > 1))
    and test_ai.id not in

-- set 2 - includes one row from each set of duplicates
(select min(id)
from test_ai as F
WHERE EXISTS (select ruleid, title, count(id)
from test_ai
WHERE test_ai.title = F.title 
    AND test_ai.ruleid = F.ruleid
group by test_ai.title, test_ai.ruleid
HAVING count(test_ai.id) > 1)   
GROUP BY title, ruleid
)

此SQL标识了应删除的一些行（第2,6,7行），但它确实按“打开日期”选择了最旧的文章。（应该删除行2,5,6）我意识到我没有在声明中指定这个，但我正在努力解决如何添加这个最后一块。如果它导致我需要多次运行的脚本，以便在有多个重复项时删除重复项，那么这不是问题。

实际问题要复杂得多，但是如果我能够通过这个阻挡部分，我将能够再次前进。谢谢你看看！

Answer 1

在SQL Server 2005+中从一组（或一组中的每个组）中删除一行的典型模型是：

;WITH cte AS 
(
  SELECT col, rn = ROW_NUMBER() OVER 
    (PARTITION BY something ORDER BY something)
  FROM dbo.base_table
  WHERE ...
)
DELETE x WHERE rn = 1;

在你的情况下，这将是：

;WITH cte AS 
(
  SELECT id, ruleid, Title, rn = ROW_NUMBER() OVER 
  (
     PARTITION BY ruleid, Title  
     ORDER BY auditdata_whencreated DESC
  )
  FROM dbo.test_ai
)
DELETE cte 
  OUTPUT deleted.id
  WHERE rn > 1;

结果：

id
----
2
6
5

删除重复项 - 仅包括除最近日期之外的所有行

1 个答案: