How to remove duplicate rows in SQL Server 2005 when no key is present
This tip describes how to delete duplicate rows from a table that doesn't have a key.
An easy way to remove duplicate rows from a table in SQL Server 2005 is to use undocumented feature called
Note that this feature is undocumented and unsupported so use at your own risk!
A simple test-case. Create a test table:
For more information about
For SQL Server 2008 equivalent, see: How to remove duplicate rows in SQL Server 2008 when no key is present[^].
%%lockres%%
. 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 %%lockres%%
:DELETE
FROM TestTable
WHERE TestTable.%%lockres%%
NOT IN (SELECT MIN(b.%%lockres%%)
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%%
, corresponding SQL Server 2008 pseudo column, see: Physical location of a row in SQL Server[^].For SQL Server 2008 equivalent, see: How to remove duplicate rows in SQL Server 2008 when no key is present[^].