PostgreSQL – Specify Primary Key Number Space

Postgres has sequences, and you can definitely use more than 1 of them for the same table. For example, the following code generates value for invoiceNumber column based on invoiceType in the trigger :

create sequence seq_1;
create sequence seq_2;

create table table1(invoiceType varchar(10) not null,
invoiceNumber int not null,
constraint PK_table1 PRIMARY KEY (invoiceType,invoiceNumber),
constraint CHK_invoiceType CHECK (invoiceType IN ('Type1','Type2')));

CREATE OR REPLACE FUNCTION table1_seq_generator() RETURNS trigger AS $body_start$
    BEGIN
        IF NEW.invoiceType = 'Type1' THEN 
          NEW.invoiceNumber := nextval('seq_1');
        ELSIF NEW.invoiceType ='Type2' THEN
          NEW.invoiceNumber := nextval('seq_2');
        END IF;
        RETURN NEW;
    END;
$body_start$ LANGUAGE plpgsql;

CREATE TRIGGER biTable1 BEFORE INSERT ON table1
FOR EACH ROW
WHEN (NEW.invoiceNumber IS NULL) 
   EXECUTE PROCEDURE table1_seq_generator();

---------------Testing ----------------------------
   INSERT INTO table1(invoiceType) values ('Type1');
   INSERT INTO table1(invoiceType) values ('Type2');
   INSERT INTO table1(invoiceType) values ('Type1');
   INSERT INTO table1(invoiceType) values ('Type2');
   SELECT * FROM table1;

You don't necessary have to do it in trigger, application code itself can get nextval for different sequence.

Also, I'd not use invoiceType,invoiceNumber as primary key constraint, but rather have surrogate pk and unique constraint on invoiceType,invoiceNumber (or branch,invoiceNumber according to your naming ).

For a table created like this:

CREATE TABLE public.delete_key_bigserial (id bigserial PRIMARY KEY NOT NULL);

... both my queries in the previous answer (as well as pgAdmin, psql or any other decent client) would find the PK constraint. If it's not there, you removed it somehow.
Note that my first query only returns the column if it is the PK and a serial type - which is the case for the example.

Another possible cause for the confusion: Maybe you have more than one table named delete_key_bigserial in your database? Table names are only unique inside a single schema. Test with:

SELECT * FROM pg_class WHERE relname = 'delete_key_bigserial';

To make your query unambiguous, schema-qualify the table name:

WHERE  a.attrelid = 'public.delete_key_bigserial'::regclass

There are ways to make the constraint "disappear" without leaving a DROP CONSTRAINT in your logs.

• Drop and recreate the table.
• Drop and recreate the schema or database.
• (Temporarily) set log_statement or other relevant settings so the statement is not logged.
• Manipulate the system catalogs directly (as superuser) Internally, the primary key is set with contype = 'p' in the table pg_constraint.

• Edit the log files.

• etc.