So what's wrong with my solution?

Your solution, I'm afraid, is logically flawed. Eg if this is sample data

T1 (CustNo, OrderNo)

1,1

1,2

2,1

T2 (CustNo, OrderNo)

1,1

Your query...

So are you thinking of adding a new column to the 'old' table corresponding with 'software_no' in the new table?

Once you have the 'next' identity number, what are you going to do with it?

Maybe @@IDENTITY, or Scope_Identity() (check BOL for details) will give you what you need?

Your idea is probably the way I would do it.

The tricky bit is the creation of the mapping table. Perhaps you can partially automate this, by matching on 'test description'...

select t1.*

from t1 left join t2 on t1.Custno = t2.CustNo and t1.OrderNo = t2.OrderNo

where t2.CustNo is null and t2.OrderNo is null

Why do you want to return every single field, in every single record, for such a large table?

A clustered index will help if you run a query with a suitable...

Yes it matters (see next para). The triggers will fire as usual, because they are defined at table level. So you need to avoid importing into those tables that will...

Maybe you could create a trigger that would perform the integrity checks that you need on insert, update etc.

So what is the DTS package transferring? Not records, I presume. Why do you want to call triggers when they look after themselves after inserts/updates etc?

You'll have to be a...

This code reproduces the error - could it be the problem?

declare @contact varchar(10)

set @contact = 'abbbbbbbbc '

select substring(@contact,1,charindex(' ',@contact)-1)

Hang on. VARCHAR value 'NULL'?? Suggests that this might work:

select * from tableA

where col5 = 'NULL'

If so, it's not empty - it's a string set to NULL.

The entries are not NULL. What makes you think they are? Are you sure they're not just empty ('')?

Your syntax is fine - and very simple. Try inverting the query

select * from tableA

where col5 is not NULL

and see whether the 'blanks' are returned.

I think that your understanding is wrong this time - NULLs are fine in FK constraints - at least in SQL Server (BOL confirms).

Sounds like the SQL Server service is running under the sys admin account. Find MSSQLServer in Admin Tools / Services and right click - select Properties and then the Log...