PostgreSQL Reference Manual - Volume 1 - SQL Language Reference by The PostgreSQL Global Development Group Paperback (6"x9"), 716 pages ISBN 0954612027 RRP £32.00 ($49.95) Sales of this book support the PostgreSQL project! Get a printed copy>>>

PostgreSQL Reference Manual Volume 1 Buy the book here! >>> support free software

3.7 Schemas

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, joe in two databases in the same cluster; but the system can be configured to allow joe access 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 example, both schema1 and myschema may contain tables named mytable. Unlike databases, schemas are not rigidly separated: a user may 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 cannot collide with the names of other objects.

Schemas are analogous to directories at the operating system level, except that schemas cannot be nested.