如何删除重复的行? [英] How can I remove duplicate rows?

问题描述

从相当大的 SQL Server 表(即 300,000+ 行)中删除重复行的最佳方法是什么?

What is the best way to remove duplicate rows from a fairly large SQL Server table (i.e. 300,000+ rows)?

当然，由于 RowID 标识字段的存在，这些行不会完全重复.

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

推荐答案

假设没有空值，你 GROUP BY 唯一列，SELECT MIN (或 MAX) RowId 作为要保留的行.然后，删除所有没有行 ID 的内容:

Assuming no nulls, you GROUP BY the unique columns, and SELECT the MIN (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

如果你有一个 GUID 而不是整数，你可以替换

In case you have a GUID instead of an integer, you can replace

MIN(RowId)

与

CONVERT(uniqueidentifier, MIN(CONVERT(char(36), MyGuidColumn)))

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