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How to remove duplicate rows in SQL Server 2008 when no key is present

An easy way to remove duplicate rows from a table in SQL Server 2008 is to use undocumented feature called %%physloc%%. This pseudo column shows the physical location of a row.
 
Note that this feature is undocumented and unsupported so use at your own risk!
 
A simple test-case. Create a test table:
CREATE TABLE TestTable (
   Column1 varchar(1),
   Column2 int
);
Add some rows with few duplicates:
INSERT INTO TestTable VALUES ('A', 1);
INSERT INTO TestTable VALUES ('A', 1); -- duplicate
INSERT INTO TestTable VALUES ('A', 2);
INSERT INTO TestTable VALUES ('B', 1);
INSERT INTO TestTable VALUES ('B', 2);
INSERT INTO TestTable VALUES ('B', 2); -- duplicate
INSERT INTO TestTable VALUES ('C', 2);
You can select the data to see that all seven rows are present:
SELECT *
FROM   TestTable a
ORDER BY a.Column1, a.Column2;
Now let's delete the two duplicates using the %%physloc%%:
DELETE
FROM  TestTable
WHERE TestTable.%%physloc%%
      NOT IN (SELECT MIN(b.%%physloc%%)
              FROM   TestTable b
              GROUP BY b.column1, b.Column2);
And if you run the query again you'll see that only five rows remain and duplicates have been deleted.
SELECT *
FROM   TestTable a
ORDER BY a.Column1, a.Column2;
 
For more information about %%physloc%%, see Physical location of a row in SQL Server[^].
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