;WITH CTE AS
(
SELECT ROW_NUMBER() OVER(PARTITION BY SIZE ORDER BY ID)  RN , ID, SIZE FROM @table
)
DELETE FROM CTE WHERE RN <> 1

-- Create a test database
USE     master;
CREATE  DATABASE RemoveDuplicates;
GO
USE     RemoveDuplicates;
GO
-- Source table with duplicate data (must reside on the default file group)
CREATE  TABLE dbo.Data
        (
        id      INTEGER IDENTITY(1,1) NOT NULL PRIMARY KEY CLUSTERED,
        size    INTEGER NOT NULL
        ) 
        ON [DEFAULT];
GO
-- Sample data
INSERT  dbo.Data (size)
VALUES  (1), (1), (2),
        (3), (2), (1), (3);
GO
-- Sample non-clustered index
CREATE  NONCLUSTERED INDEX [IX dbo.Data size]
ON      dbo.Data (size)
ON      [DEFAULT];
GO
-- Identify the records to keep and save them to a new table
SELECT  D1.id,
        D1.size
INTO    dbo.ToSave
FROM    (
        SELECT  *,
                rn = ROW_NUMBER() OVER (PARTITION BY size ORDER BY id)
        FROM    dbo.Data D1
        ) D1
WHERE   D1.rn = 1;
GO
-- Switch to the bulk logged recovery model to allow
-- minimally-logged index builds
-- (in a real system you would take a log backup now)
ALTER   DATABASE RemoveDuplicates
SET     RECOVERY BULK_LOGGED;
GO
-- The new table needs the same indexes as the source table
-- Full requirements: http://technet.microsoft.com/en-us/library/ms191160.aspx
ALTER   TABLE dbo.ToSave
ADD     PRIMARY KEY CLUSTERED (id);
GO
CREATE  INDEX nc1 ON dbo.ToSave (size) ON [DEFAULT];
GO
-- Switch back to full recovery
-- (in a real system you would take a second log backup now)
ALTER   DATABASE RemoveDuplicates
SET     RECOVERY FULL;
GO
-- Replace the original table with the saved data
BEGIN   TRY
        -- Begin atomic operation
        BEGIN TRANSACTION;

        -- Empty the source table
        TRUNCATE TABLE dbo.Data;

        -- Transfer the saved rows (metadata operation)
        ALTER TABLE dbo.ToSave
        SWITCH TO dbo.Data;

        -- Drop the temporary storage
        DROP TABLE dbo.ToSave;

        -- Success
        COMMIT TRANSACTION;
END     TRY
BEGIN   CATCH
        -- Error handling
        DECLARE @Msg NVARCHAR(2048);
        SET     @Msg = ERROR_MESSAGE();
        IF  XACT_STATE() <> 0 ROLLBACK TRANSACTION;
        RAISERROR('ROLLBACK: %s', 16, 1, @Msg);
END     CATCH;
GO
-- Show the de-duplicated data
SELECT  *
FROM    dbo.Data;
GO
-- Tidy up
USE     master;
DROP    DATABASE RemoveDuplicates;