PostgreSQL - SQL Language Reference

PostgreSQL Reference Manual - Volume 1 - SQL Language Reference
by The PostgreSQL Global Development Group
Paperback (6"x9"), 716 pages
ISBN 0954612027
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PostgreSQL Reference Manual
Volume 1

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12.51 CREATE VIEW

Name

CREATE VIEW -- define a new view

Synopsis

CREATE [ OR REPLACE ] [ TEMP | TEMPORARY ] VIEW name [ (
 column_name [, ...] ) ]
    AS query

Description

CREATE VIEW defines a view of a query. The view is not physically materialized. Instead, the query is run every time the view is referenced in a query.

CREATE OR REPLACE VIEW is similar, but if a view of the same name already exists, it is replaced. You can only replace a view with a new query that generates the identical set of columns (i.e., same column names and data types).

If a schema name is given (for example, CREATE VIEW myschema.myview ...) then the view is created in the specified schema. Otherwise it is created in the current schema. Temporary views exist in a special schema, so a schema name may not be given when creating a temporary view. The name of the view must be distinct from the name of any other view, table, sequence, or index in the same schema.

Parameters

TEMPORARY or TEMP: If specified, the view is created as a temporary view. Temporary views are automatically dropped at the end of the current session. Existing permanent relations with the same name are not visible to the current session while the temporary view exists, unless they are referenced with schema-qualified names. If any of the tables referenced by the view are temporary, the view is created as a temporary view (whether TEMPORARY is specified or not).
name: The name (optionally schema-qualified) of a view to be created.
column_name: An optional list of names to be used for columns of the view. If not given, the column names are deduced from the query.
query: A SELECT or VALUES command which will provide the columns and rows of the view.

Notes

Currently, views are read only: the system will not allow an insert, update, or delete on a view. You can get the effect of an updatable view by creating rules that rewrite inserts, etc. on the view into appropriate actions on other tables. For more information see CREATE RULE.

Use the DROP VIEW statement to drop views.

Be careful that the names and types of the view's columns will be assigned the way you want. For example,

CREATE VIEW vista AS SELECT 'Hello World';

is bad form in two ways: the column name defaults to ?column?, and the column data type defaults to unknown. If you want a string literal in a view's result, use something like

CREATE VIEW vista AS SELECT text 'Hello World' AS hello;

Access to tables referenced in the view is determined by permissions of the view owner. However, functions called in the view are treated the same as if they had been called directly from the query using the view. Therefore the user of a view must have permissions to call all functions used by the view.

Examples

Create a view consisting of all comedy films:

CREATE VIEW comedies AS
    SELECT *
    FROM films
    WHERE kind = 'Comedy';

Compatibility

The SQL standard specifies some additional capabilities for the CREATE VIEW statement:

CREATE VIEW name [ ( column_name [, ...] ) ]
    AS query
    [ WITH [ CASCADED | LOCAL ] CHECK OPTION ]

The optional clauses for the full SQL command are:

CHECK OPTION: This option has to do with updatable views. All INSERT and UPDATE commands on the view will be checked to ensure data satisfy the view-defining condition (that is, the new data would be visible through the view). If they do not, the update will be rejected.
LOCAL: Check for integrity on this view.
CASCADED: Check for integrity on this view and on any dependent view. CASCADED is assumed if neither CASCADED nor LOCAL is specified.

CREATE OR REPLACE VIEW is a PostgreSQL language extension. So is the concept of a temporary view.