Re: How to create case insensitive unique constraint

> I want to disable dupplicate customer names in a database regardless to
> case.
>
> I tried
>
> CREATE TABLE customer ( id SERIAL, name CHARACTER(70));
>
> ALTER TABLE customer
>    ADD constraint customer_name_unique UNIQUE (UPPER(name));
>
> but this is not allowed in Postgres

As Csaba suggested, a unique functional index does the trick - here's
how I do it in something I'm working on right now:

CREATE UNIQUE INDEX gazPlaceNames_lower_PlaceName2_Index on
gazPlaceNames (lower(placeName));

You could use upper() similarly - lower() is better for Unicode data,
like mine.  Now, If I try to add an alternate casing for an existing
name, I get slapped:

 > select * from gazPlaceNames where lower(placeName) like lower('New
York');
  placenameid | placename | lang | script
-------------+-----------+------+--------
       291642 | New York  |      |
(1 row)

 > insert into gazPlaceNames  (placename) values ('NeW yOrK');
ERROR:  duplicate key violates unique constraint
"gazplacenames_lower_placename2_"

As a bonus, Postgres will use the index for selects involving
lower(placename), like the one above.

- John Burger
   MITRE