Mark Lybarger <mlybarger@xxxxxxxxx> writes: > 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; > > 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, sj$ cat q begin; create table foo (a int, b int); create unique index foox on foo (coalesce(a, 0), coalesce(b, 0)); insert into foo select 1, null; insert into foo select 1, null; sj$ psql -f q SET BEGIN CREATE TABLE CREATE INDEX INSERT 0 1 psql:q:7: ERROR: duplicate key value violates unique constraint "foox" DETAIL: Key ((COALESCE(a, 0)), (COALESCE(b, 0)))=(1, 0) already exists. sj$ > > 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- > -- Jerry Sievers Postgres DBA/Development Consulting e: postgres.consulting@xxxxxxxxxxx p: 312.241.7800 -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
