Question

As part of a migration project, we have imported data from a JDE iSeries DB2 database. An SSIS package was created to create the destination tables and import data. The import went successfully.

Now comes the problem – The customer wants Primary Keys created in the destination DB (SQL 2008 R2). The problem table in this case, would be one table that has 104 columns and 7.5 million rows of data. The PK required for this table is composite and has 7 columns.

We are considering this :

BEGIN TRANSACTION
GO
    ALTER TABLE [dbo].[F0911] ADD  CONSTRAINT [F0911_PK] PRIMARY KEY CLUSTERED 
    (
        [GLDCT] ASC,
        [GLDOC] ASC,
        [GLKCO] ASC,
        [GLDGJ] ASC,
        [GLJELN] ASC,
        [GLLT] ASC,
        [GLEXTL] ASC
    )WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
    GO
COMMIT

or this:

-- Rename existing tables
        sp_RENAME '[F0911]' , '[F0911_old]'
        GO

    -- Create new table
        SELECT * INTO F0911 FROM F0911_old WHERE 1=0
        GO

    --Create PK constraints
        ALTER TABLE [dbo].[F0911] ADD  CONSTRAINT [F0911_PK] PRIMARY KEY CLUSTERED 
        (
            [GLDCT] ASC,
            [GLDOC] ASC,
            [GLKCO] ASC,
            [GLDGJ] ASC,
            [GLJELN] ASC,
            [GLLT] ASC,
            [GLEXTL] ASC
        )WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
        GO

    --Insert data into new tables
        INSERT INTO F0911
        SELECT * FROM F0911_old
        GO

    -- Drop old tables
        DROP TABLE F0911_old
        GO

Which would be a more efficient approach, performance wise? I have a gut feeling that both are the same and even the first approach does the same thing as the second one does, implicitly. Is this understanding correct?

Please note that all these columns already exist in the table and we cannot modify the table definition.

Thanks,
Raj

Answer 1

They’re the same. The effect of creating a clustered index is to arrange the pages which will happen in both cases. For non-clustered indexes it will help to disable the index and then turn it back on and rebuilding it.