|The PostgreSQL 9.0 Reference Manual - Volume 1A - SQL Language Reference
by The PostgreSQL Global Development Group
Paperback (6"x9"), 454 pages
RRP £14.95 ($19.95)
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A PostgreSQL database cluster contains one or more named databases. Users and groups of users are shared across the entire cluster, but no other data is shared across databases. Any given client connection to the server can access only the data in a single database, the one specified in the connection request.
Note: Users of a cluster do not necessarily have the privilege to access every database in the cluster. Sharing of user names means that there cannot be different users named, say,
joein two databases in the same cluster; but the system can be configured to allow
joeaccess to only some of the databases.
A database contains one or more named schemas, which
in turn contain tables. Schemas also contain other kinds of named
objects, including data types, functions, and operators. The same
object name can be used in different schemas without conflict; for
contain tables named
mytable. Unlike databases,
schemas are not rigidly separated: a user can access objects in any
of the schemas in the database he is connected to, if he has
privileges to do so.
There are several reasons why one might want to use schemas:
- To allow many users to use one database without interfering with each other.
- To organize database objects into logical groups to make them more manageable.
- Third-party applications can be put into separate schemas so they do not collide with the names of other objects.
Schemas are analogous to directories at the operating system level, except that schemas cannot be nested.
|ISBN 9781906966041||The PostgreSQL 9.0 Reference Manual - Volume 1A - SQL Language Reference||See the print edition|