Background
If some columns in one or more tables in a database are frequently searched for, an administrator can define a view for these columns, and then users can directly access these columns in the view without entering search criteria.
A view is different from a base table. It is only a virtual object rather than a physical one. Only view definition is stored in the database and view data is not. The data is stored in a base table. If data in the base table changes, the data in the view changes accordingly. In this sense, a view is like a window through which users can know their interested data and data changes in the database. A view is triggered every time it is referenced.
Managing Views
Creating a view
Run the following command to create MyView:
""
postgres=# CREATE OR REPLACE VIEW MyView AS SELECT * FROM tpcds.web_returns WHERE trunc(wr_refunded_cash) > 10000;
CREATE VIEW
NOTE:
The OR REPLACE parameter in this command is optional. It indicates that if the view exists, the new view will replace the existing view.
Querying a view
Run the following command to query MyView:
""
SELECT * FROM MyView;
Viewing details about a specified view
Run the following command to view details about the dba_users view:
""
postgres=# \d+ dba_users
View "PG_CATALOG.DBA_USERS"
Column | Type | Modifiers | Storage | Description
----------+-----------------------+-----------+----------+-------------
USERNAME | CHARACTER VARYING(64) | | extended |
View definition:
SELECT PG_AUTHID.ROLNAME::CHARACTER VARYING(64) AS USERNAME
FROM PG_AUTHID;
Deleting a view
Run the following command to delete MyView:
""
postgres=# DROP VIEW MyView;
DROP VIEW
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