Creating and Managing Schemas

    Every database has a default schema named public. If you do not create any schemas, objects are created in the public schema. All database roles (users) have and USAGE privileges in the public schema. When you create a schema, you grant privileges to your users to allow access to the schema.

    Use the CREATE SCHEMA command to create a new schema. For example:

    To create or access objects in a schema, write a qualified name consisting of the schema name and table name separated by a period. For example:

    1. myschema.table

    You can create a schema owned by someone else, for example, to restrict the activities of your users to well-defined namespaces. The syntax is:

    1. => CREATE SCHEMA schemaname AUTHORIZATION username;

    To specify an object’s location in a database, use the schema-qualified name. For example:

    You can set the search_path configuration parameter to specify the order in which to search the available schemas for objects. The schema listed first in the search path becomes the default schema. If a schema is not specified, objects are created in the default schema.

    1. => ALTER DATABASE mydatabase SET search_path TO myschema,
    2. public, pg_catalog;

    Viewing the Current Schema

    Use the current_schema() function to view the current schema. For example:

      Use the SHOW command to view the current search path. For example:

      Use the DROP SCHEMA command to drop (delete) a schema. For example:

      1. => DROP SCHEMA myschema CASCADE;

      The following system-level schemas exist in every database:

      • pg_catalog contains the system catalog tables, built-in data types, functions, and operators. It is always part of the schema search path, even if it is not explicitly named in the search path.
      • information_schema consists of a standardized set of views that contain information about the objects in the database. These views get system information from the system catalog tables in a standardized way.
      • pg_toast stores large objects such as records that exceed the page size. This schema is used internally by the HAWQ system.
      • hawq_toolkit is an administrative schema that contains external tables, views, and functions that you can access with SQL commands. All database users can access to view and query the system log files and other system metrics.