Note: The following description applies both to Postgres-XC and PostgreSQL if not described explicitly. You can read PostgreSQL as Postgres-XC except for version number, which is specific to each product.
In the sections that follow, we will discuss how you can extend the PostgreSQL SQL query language by adding:
functions (starting in Section 34.3)
aggregates (starting in Section 34.10)
data types (starting in Section 34.11)
operators (starting in Section 34.12)
operator classes for indexes (starting in Section 34.14)
packages of related objects (starting in Section 34.15)