How to delete duplicate rows in sql server?

Question

How can I delete duplicate rows where no unique row id exists?

My table is

col1  col2 col3 col4 col5 col6 col7
john  1    1    1    1    1    1 
john  1    1    1    1    1    1
sally 2    2    2    2    2    2
sally 2    2    2    2    2    2

I want to be left with the following after the duplicate removal:

john  1    1    1    1    1    1
sally 2    2    2    2    2    2

I've tried a few queries but i think they depend on a row id as I don't get desired result. For example:

DELETE FROM table WHERE col1 IN (
    SELECT id FROM table GROUP BY id HAVING ( COUNT(col1) > 1 )
)

Answer 1

If you have no references, like foreign keys, you can do this. I do it a lot when testing proofs of concept and the test data gets duplicated.

SELECT DISTINCT [col1],[col2],[col3],[col4],[col5],[col6],[col7]

INTO [newTable]

;

Go into the object explorer and delete the old table.

Rename the new table with the old table's name.

Answer 2

with myCTE
as

(
select productName,ROW_NUMBER() over(PARTITION BY productName order by slno) as Duplicate from productDetails
)
Delete from myCTE where Duplicate>1

Answer 3

If you have the ability to add a column to the table temporarily, this was a solution that worked for me:

ALTER TABLE dbo.DUPPEDTABLE ADD RowID INT NOT NULL IDENTITY(1,1)

Then perform a DELETE using a combination of MIN and GROUP BY

DELETE b
FROM dbo.DUPPEDTABLE b
WHERE b.RowID NOT IN (
                     SELECT MIN(RowID) AS RowID
                     FROM dbo.DUPPEDTABLE a WITH (NOLOCK)
                     GROUP BY a.ITEM_NUMBER,
                              a.CHARACTERISTIC,
                              a.INTVALUE,
                              a.FLOATVALUE,
                              a.STRINGVALUE
                 );

Verify that the DELETE performed correctly:

SELECT a.ITEM_NUMBER,
    a.CHARACTERISTIC,
    a.INTVALUE,
    a.FLOATVALUE,
    a.STRINGVALUE, COUNT(*)--MIN(RowID) AS RowID
FROM dbo.DUPPEDTABLE a WITH (NOLOCK)
GROUP BY a.ITEM_NUMBER,
    a.CHARACTERISTIC,
    a.INTVALUE,
    a.FLOATVALUE,
    a.STRINGVALUE
ORDER BY COUNT(*) DESC 

The result should have no rows with a count greater than 1. Finally, remove the rowid column:

ALTER TABLE dbo.DUPPEDTABLE DROP COLUMN RowID;