CREATE TYPE CUSTOMER_TYPE AS ENUM
('enum1', 'enum2', 'enum3', '...', 'enum15');       ## max lenght of enum names ~15

CREATE TABLE CUSTOMER(
   CUSTOMER_ONE    TEXT PRIMARY KEY NOT NULL,       ## max 35 char String
   ATTRIBUTE_ONE   TEXT UNIQUE,                     ## max 35 char String
   ATTRIBUTE_TWO   TEXT,                            ## 1-80 char String
   PRIVATEKEYTYPE  CUSTOMER_TYPE                    ## see enum
);

select * from customer
where Customer_One='XXX' OR Attribute_One='XXX';

CREATE TABLE customer (
   privatekeytype customer_type     -- move the enum to 1st pos to save some more
 , customer_one   text PRIMARY KEY
 , attribute_two  text
);

CREATE INDEX customer_attribute_one_idx ON customer (hash(customer_one));

SELECT *
FROM   customer
WHERE  'XXX' IN (customer_one, hash(customer_one));

->  BitmapOr  (cost=5.34..5.34 rows=5 width=0)
       ->  Bitmap Index Scan on customer_pkey  (cost=0.00..2.66 rows=1 width=0)
             Index Cond: ('XXX'::text = customer.customer_one)
       ->  Bitmap Index Scan on customer_attribute_one_idx  (cost=0.00..2.68 rows=4 width=0)
             Index Cond: ('XXX'::text = hash(customer.customer_one))