Key value pair in PostgreSQL [closed]

Answer 1

You need to install the additional module hstore before you can use it. Once per database:

CREATE EXTENSION hstore;

CREATE EXTENSION has been introduced with Postgres 9.1. Older versions have other methods.

Read more about the pros and (many) cons of EAV (Entity-Attribute-Value) storage in an RDBMS under this related question od dba.SE.