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Chapter 4. The
Query Language |
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The fundamental notion in Postgres is that of a class, which is
a named collection of object instances. Each instance has the same
collection of named attributes, and each attribute is of a specific
type. Furthermore, each instance has a permanent object identifier (OID) that is unique throughout
the installation. Because SQL syntax refers to tables, we will use
the terms table and class interchangeably. Likewise, an SQL row is an instance and SQL
columns are attributes. As previously discussed, classes are
grouped into databases, and a collection of databases managed by a
single postmaster process constitutes an installation or site.