On Wed, Jul 20, 2016 at 8:14 PM, Mark Lybarger <mlybar...@gmail.com> wrote:
> I have a relation such as > create table order_item ( id uuid not null primary key, order_id number > not null, item_code text, make text, model text, reason text, size text, > expiration_date timestamp ); > > where the combination of the columns order_id, item_code, make, model, > reason, size must be unique (unless there's an expiration date). > > I'm inclined to use a unique index: > > create unique index unique_index_order_item_1 on order_item (order_id, > item_code, make, model, reason, size) > where expiration_date is null; > You can also: create unique index unique_index_order_item_1 on order_item (coalesce(order_id, -1), coalesce(item_code, -1), coalesce(make, '--NULL--), coalesce(model, '--NULL--), coalesce(reason, '--NULL--), coalesce(size, '--NULL--'), coalesce(expiration_date, '1700-01-01 00:00:00')); > > this works as expected and the duplicate row is rejected > : > insert into order_item ( 1, 88, 'CODE', 'MAKE','MODEL','REASON', 'SIZE', > null); <- first adds > insert into order_item ( 1, 88, 'CODE', 'MAKE','MODEL','REASON', 'SIZE', > null); <- rejects > > however, nulls are allowed for all the columns except the order_id. so, > when I add a null value, it fails to meet my expectations, > > insert into order_item ( 1, 88, 'CODE', 'MAKE',null,'REASON', 'SIZE', > null); <- first adds > insert into order_item ( 1, 88, 'CODE', 'MAKE',null,'REASON', 'SIZE', > null); <- adds, but should reject. > > This leads me to think I need to create 2^5 or 32 unique constraints to > handle the various combinations of data that I can store. Until now, this > integrity is handled in the application code. That breaks when the > application is multi-threaded and the rules are not applied at the database > level. > > Another solution I can think of is to just use a trigger to prevent the > duplicate rows. > > Any thoughts are certainly appreciated. I can't do much about the data > model itself right now, I need to protect the integrity of the data. > > Thanks! > -mark- > > > > > > -- Best Wishes, Chris Travers Efficito: Hosted Accounting and ERP. Robust and Flexible. No vendor lock-in. http://www.efficito.com/learn_more
