PostgreSQL 8.2.9 Enum Type

Question

PostgreSQL from 8.3 knows Enumerated Types.

Simple question: Does 8.2(.9) know them too? If not, what can be used as replacement?

Answer 1

Enumerated types are not supported in 8.2.

As an alternative, use a text column with a foreign key reference to a table that lists possible values.

CREATE TABLE fruit_enum (
    fruit text primary key
);

INSERT INTO fruit_enum(fruit) VALUES
('apple'),('pear'),('grape');

CREATE TABLE basket (
    -- ... blah columns ...
    fruit text,
    -- ... blah columns ...
    CONSTRAINT fruit_fk FOREIGN KEY (fruit) REFERENCES fruit_enum(fruit)
);

This is the classic relational formulation, and is usually preferable to using an enum anyway. Enumerations are painful to deal with from some client applications and Pg doesn't currently support removing values from them either.

Here's how the above works:

regress=# INSERT INTO basket(fruit) VALUES ('apple');
INSERT 0 1
regress=# INSERT INTO basket(fruit) VALUES ('cider');
ERROR:  insert or update on table "basket" violates foreign key constraint "fruit_fk"
DETAIL:  Key (fruit)=(cider) is not present in table "fruit_enum".
regress=# 

If you like you can indirect the enumeration via an integer ID, where the foreign key is to the enumeration table's ID not the enumeration value. Personally I'm not a fan of that approach, even though it's really only a true "enumeration" that way, because getting the value always requires an expensive JOIN or subquery, and there's typically little space saved.

Alternately, as @a_horse_with_no_name pointed out, a simple CHECK constraint is often sufficient:

CREATE TABLE basket (
    -- ... blah columns ...
    fruit text,
    -- ... blah columns ...
    CONSTRAINT fruit_in_allowed_list CHECK (fruit IN ('apple', 'pear', 'grape'))
);

Like the foreign key approach (but unlike enums) this is SQL-standard and should work on any database.

Also, seriously, 8.2? That's end-of-life and woefully, amazingly out of date. Make urgent upgrade plans.

Answer 2

Enums were introduced in 8.3
Here are the release notes: http://www.postgresql.org/docs/8.3/static/release-8-3.html

The data types for 8.2 are documented here: http://www.postgresql.org/docs/8.2/static/datatype.html

But you shouldn't use 8.2 anyway (actually I wouldn't recommend 8.3 either)