Can I delete database duplicates based on multiple columns?

Question

I asked this question a while back to delete duplicate records based on a column. The answer worked great:

delete from tbl
where id NOT in
(
select  min(id)
fro         


        

Answer 1

Try this one. I created a table tblA with three columns.

CREATE TABLE tblA
(
id int IDENTITY(1, 1),
colA int, 
colB int, 
colC int
)

And added some duplicate values.

INSERT INTO tblA VALUES (1, 2, 3)
INSERT INTO tblA VALUES (1, 2, 3)
INSERT INTO tblA VALUES (4, 5, 6)
INSERT INTO tblA VALUES (7, 8, 9)
INSERT INTO tblA VALUES (7, 8, 9)

If you replace the select with a delete in the statement below you will have your multiple column delete working.

SELECT MIN(Id) as id
FROM
(
SELECT COUNT(*) as aantal, a.colA, a.colB, a.colC
FROM tblA       a
INNER JOIN tblA b   ON b.ColA = a.ColA
                    AND b.ColB = a.ColB
                    AND b.ColC = a.ColC
GROUP BY a.id, a.colA, a.colB, a.colC
HAVING COUNT(*) > 1
) c
INNER JOIN tblA d ON d.ColA = c.ColA
                    AND d.ColB = c.ColB
                    AND d.ColC = c.ColC
GROUP BY d.colA, d.colB, d.colC