Question

I have a Constraint on a table with IGNORE_DUP_KEY. This allows bulk inserts to partially work where some records are dupes and some are not (only inserting the non-dupes). However, it does not allow updates to partially work, where I only want those records updated where dupes will not be created.

Does anyone know how I can support IGNORE_DUP_KEY when applying updates?

I am using MS SQL 2005

Answer 1

If I understand correctly, you want to do UPDATEs without specifying the necessary WHERE logic to avoid creating duplicates?

create table #t (col1 int not null, col2 int not null, primary key (col1, col2))

insert into #t 
select 1, 1 union all 
select 1, 2 union all 
select 2, 3

-- you want to do just this...
update #t set col2 = 1

-- ... but you really need to do this
update #t set col2 = 1
where not exists (
    select * from #t t2
    where #t.col1 = t2.col1 and col2 = 1
    )

The main options that come to mind are:

1. Use a complete UPDATE statement to avoid creating duplicates
2. Use an INSTEAD OF UPDATE trigger to ‘intercept’ the UPDATE and only do UPDATEs that won’t create a duplicate
3. Use a row-by-row processing technique such as cursors and wrap each UPDATE in TRY…CATCH… or whatever the language’s equivalent is

I don’t think anyone can tell you which one is best, because it depends on what you’re trying to do and what environment you’re working in. But because row-by-row processing could potentially produce some false positives, I would try to stick with a set-based approach.