如何删除重复行? [英] How can I remove duplicate rows?
本文介绍了如何删除重复行?的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
从相当大的表(即300,000+行)中删除重复行的最佳方法是什么?
当然这些行不会是完美的重复,因为存在RowID身份字段。
MyTable
-----------
RowID int not null identity(1,1)主键,
Col1 varchar(20)not null,
Col2 varchar(2048)not null,
Col3 tinyint not null
解决方案
假设没有null,你 GROUP BY
唯一列,而 SELECT
MIN(或MAX)
RowId作为要保留的行。然后,只需删除没有行ID的所有内容:
从MyTable
中删除B $ b LEFT OUTER JOIN b $ b SELECT MIN(RowId)作为RowId,Col1,Col2,Col3
FROM MyTable
GROUP BY Col1,Col2,Col3
)作为KeepRows ON
MyTable.RowId = KeepRows .RowId
WHERE
KeepRows.RowId IS NULL
如果您有GUID而不是整数,您可以替换
MIN(RowId)
pre>
与
CONVERT(uniqueidentifier,MIN(CONVERT (36),MyGuidColumn)))
What is the best way to remove duplicate rows from a fairly large table (i.e. 300,000+ rows)?
The rows of course will not be perfect duplicates because of the existence of the RowID identity field.
MyTable ----------- RowID int not null identity(1,1) primary key, Col1 varchar(20) not null, Col2 varchar(2048) not null, Col3 tinyint not null
解决方案Assuming no nulls, you
GROUP BY
the unique columns, andSELECT
theMIN (or MAX)
RowId as the row to keep. Then, just delete everything that didn't have a row id:DELETE FROM MyTable LEFT OUTER JOIN ( SELECT MIN(RowId) as RowId, Col1, Col2, Col3 FROM MyTable GROUP BY Col1, Col2, Col3 ) as KeepRows ON MyTable.RowId = KeepRows.RowId WHERE KeepRows.RowId IS NULL
In case you have a GUID instead of an integer, you can replace
MIN(RowId)
with
CONVERT(uniqueidentifier, MIN(CONVERT(char(36), MyGuidColumn)))
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