Note: With the release of Postgres 9.4 and JSONB, in most cases it becomes a better approach than simply HStore. For a more in depth comparisson you can check out this post by Citus Data

What is it

HStore is a key value store within Postgres. You can use it similar to how you would use a dictionary within another language, though it's specific to a column on a row.

Enabling HStore

To enable HStore on your database you run:

CREATE EXTENSION hstore;

Creating an hStore column

To create a field in a table with the hstore datatype simply use hstore as the column type:

CREATE TABLE products (
  id serial PRIMARY KEY,
  name varchar,
  attributes hstore
);

Inserting data

To insert data you would include it all within single quotes as you would for a text field. The difference with hstore is some extra structure so it knows how to create the dictionary:

INSERT INTO products (name, attributes) VALUES (
 'Geek Love: A Novel',
 'author    => "Katherine Dunn",
  pages     => 368,
  category  => fiction'
 );

Retrieving data

SELECT name, attributes->'author' as author
FROM products
WHERE attributes->'category' = 'fiction'