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);
INSERT INTO TestTable VALUES ('A', 2);
INSERT INTO TestTable VALUES ('B', 1);
INSERT INTO TestTable VALUES ('B', 2);
INSERT INTO TestTable VALUES ('B', 2);
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[
^].