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CREATE VIEW(7)		PostgreSQL 9.5.0 Documentation		CREATE VIEW(7)

NAME
       CREATE_VIEW - define a new view

SYNOPSIS
       CREATE [ OR REPLACE ] [ TEMP | TEMPORARY ] [ RECURSIVE ] VIEW name [ ( column_name [, ...] ) ]
	   [ WITH ( view_option_name [= view_option_value] [, ... ] ) ]
	   AS query
	   [ WITH [ CASCADED | LOCAL ] CHECK OPTION ]

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. The new query must generate the same
       columns that were generated by the existing view query (that is, the
       same column names in the same order and with the same data types), but
       it may add additional columns to the end of the list. The calculations
       giving rise to the output columns may be completely different.

       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 cannot be given when creating a temporary
       view. The name of the view must be distinct from the name of any other
       view, table, sequence, index or foreign table 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).

       RECURSIVE
	   Creates a recursive view. The syntax

	       CREATE RECURSIVE VIEW name (columns) AS SELECT ...;

	   is equivalent to

	       CREATE VIEW name AS WITH RECURSIVE name (columns) AS (SELECT ...) SELECT columns FROM name;

	   A view column list must be specified for a recursive view.

       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.

       WITH ( view_option_name [= view_option_value] [, ... ] )
	   This clause specifies optional parameters for a view; the following
	   parameters are supported:

	   check_option (string)
	       This parameter may be either local or cascaded, and is
	       equivalent to specifying WITH [ CASCADED | LOCAL ] CHECK OPTION
	       (see below). This option can be changed on existing views using
	       ALTER VIEW (ALTER_VIEW(7)).

	   security_barrier (boolean)
	       This should be used if the view is intended to provide
	       row-level security. See Section 38.5, “Rules and Privileges”,
	       in the documentation for full details.

       query
	   A SELECT(7) or VALUES(7) command which will provide the columns and
	   rows of the view.

       WITH [ CASCADED | LOCAL ] CHECK OPTION

	   This option controls the behavior of automatically updatable views.
	   When this option is specified, INSERT and UPDATE commands on the
	   view will be checked to ensure that new rows satisfy the
	   view-defining condition (that is, the new rows are checked to
	   ensure that they are visible through the view). If they are not,
	   the update will be rejected. If the CHECK OPTION is not specified,
	   INSERT and UPDATE commands on the view are allowed to create rows
	   that are not visible through the view. The following check options
	   are supported:

	   LOCAL
	       New rows are only checked against the conditions defined
	       directly in the view itself. Any conditions defined on
	       underlying base views are not checked (unless they also specify
	       the CHECK OPTION).

	   CASCADED
	       New rows are checked against the conditions of the view and all
	       underlying base views. If the CHECK OPTION is specified, and
	       neither LOCAL nor CASCADED is specified, then CASCADED is
	       assumed.

	   The CHECK OPTION may not be used with RECURSIVE views.

	   Note that the CHECK OPTION is only supported on views that are
	   automatically updatable, and do not have INSTEAD OF triggers or
	   INSTEAD rules. If an automatically updatable view is defined on top
	   of a base view that has INSTEAD OF triggers, then the LOCAL CHECK
	   OPTION may be used to check the conditions on the automatically
	   updatable view, but the conditions on the base view with INSTEAD OF
	   triggers will not be checked (a cascaded check option will not
	   cascade down to a trigger-updatable view, and any check options
	   defined directly on a trigger-updatable view will be ignored). If
	   the view or any of its base relations has an INSTEAD rule that
	   causes the INSERT or UPDATE command to be rewritten, then all check
	   options will be ignored in the rewritten query, including any
	   checks from automatically updatable views defined on top of the
	   relation with the INSTEAD rule.

NOTES
       Use the DROP VIEW (DROP_VIEW(7)) 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. In some cases, this can be used to provide secure but
       restricted access to the underlying tables. However, not all views are
       secure against tampering; see Section 38.5, “Rules and Privileges”, in
       the documentation for details. 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.

       When CREATE OR REPLACE VIEW is used on an existing view, only the
       view's defining SELECT rule is changed. Other view properties,
       including ownership, permissions, and non-SELECT rules, remain
       unchanged. You must own the view to replace it (this includes being a
       member of the owning role).

   Updatable Views
       Simple views are automatically updatable: the system will allow INSERT,
       UPDATE and DELETE statements to be used on the view in the same way as
       on a regular table. A view is automatically updatable if it satisfies
       all of the following conditions:

       ·   The view must have exactly one entry in its FROM list, which must
	   be a table or another updatable view.

       ·   The view definition must not contain WITH, DISTINCT, GROUP BY,
	   HAVING, LIMIT, or OFFSET clauses at the top level.

       ·   The view definition must not contain set operations (UNION,
	   INTERSECT or EXCEPT) at the top level.

       ·   The view's select list must not contain any aggregates, window
	   functions or set-returning functions.

       An automatically updatable view may contain a mix of updatable and
       non-updatable columns. A column is updatable if it is a simple
       reference to an updatable column of the underlying base relation;
       otherwise the column is read-only, and an error will be raised if an
       INSERT or UPDATE statement attempts to assign a value to it.

       If the view is automatically updatable the system will convert any
       INSERT, UPDATE or DELETE statement on the view into the corresponding
       statement on the underlying base relation.  INSERT statements that have
       an ON CONFLICT UPDATE clause are fully supported.

       If an automatically updatable view contains a WHERE condition, the
       condition restricts which rows of the base relation are available to be
       modified by UPDATE and DELETE statements on the view. However, an
       UPDATE is allowed to change a row so that it no longer satisfies the
       WHERE condition, and thus is no longer visible through the view.
       Similarly, an INSERT command can potentially insert base-relation rows
       that do not satisfy the WHERE condition and thus are not visible
       through the view (ON CONFLICT UPDATE may similarly affect an existing
       row not visible through the view). The CHECK OPTION may be used to
       prevent INSERT and UPDATE commands from creating such rows that are not
       visible through the view.

       If an automatically updatable view is marked with the security_barrier
       property then all the view's WHERE conditions (and any conditions using
       operators which are marked as LEAKPROOF) will always be evaluated
       before any conditions that a user of the view has added. See Section
       38.5, “Rules and Privileges”, in the documentation for full details.
       Note that, due to this, rows which are not ultimately returned (because
       they do not pass the user's WHERE conditions) may still end up being
       locked.	EXPLAIN can be used to see which conditions are applied at the
       relation level (and therefore do not lock rows) and which are not.

       A more complex view that does not satisfy all these conditions is
       read-only by default: the system will not allow an insert, update, or
       delete on the view. You can get the effect of an updatable view by
       creating INSTEAD OF triggers on the view, which must convert attempted
       inserts, etc. on the view into appropriate actions on other tables. For
       more information see CREATE TRIGGER (CREATE_TRIGGER(7)). Another
       possibility is to create rules (see CREATE RULE (CREATE_RULE(7))), but
       in practice triggers are easier to understand and use correctly.

       Note that the user performing the insert, update or delete on the view
       must have the corresponding insert, update or delete privilege on the
       view. In addition the view's owner must have the relevant privileges on
       the underlying base relations, but the user performing the update does
       not need any permissions on the underlying base relations (see Section
       38.5, “Rules and Privileges”, in the documentation).

EXAMPLES
       Create a view consisting of all comedy films:

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

       This will create a view containing the columns that are in the film
       table at the time of view creation. Though * was used to create the
       view, columns added later to the table will not be part of the view.

       Create a view with LOCAL CHECK OPTION:

	   CREATE VIEW universal_comedies AS
	       SELECT *
	       FROM comedies
	       WHERE classification = 'U'
	       WITH LOCAL CHECK OPTION;

       This will create a view based on the comedies view, showing only films
       with kind = 'Comedy' and classification = 'U'. Any attempt to INSERT or
       UPDATE a row in the view will be rejected if the new row doesn't have
       classification = 'U', but the film kind will not be checked.

       Create a view with CASCADED CHECK OPTION:

	   CREATE VIEW pg_comedies AS
	       SELECT *
	       FROM comedies
	       WHERE classification = 'PG'
	       WITH CASCADED CHECK OPTION;

       This will create a view that checks both the kind and classification of
       new rows.

       Create a view with a mix of updatable and non-updatable columns:

	   CREATE VIEW comedies AS
	       SELECT f.*,
		      country_code_to_name(f.country_code) AS country,
		      (SELECT avg(r.rating)
		       FROM user_ratings r
		       WHERE r.film_id = f.id) AS avg_rating
	       FROM films f
	       WHERE f.kind = 'Comedy';

       This view will support INSERT, UPDATE and DELETE. All the columns from
       the films table will be updatable, whereas the computed columns country
       and avg_rating will be read-only.

       Create a recursive view consisting of the numbers from 1 to 100:

	   CREATE RECURSIVE VIEW nums_1_100 (n) AS
	       VALUES (1)
	   UNION ALL
	       SELECT n+1 FROM nums_1_100 WHERE n < 100;

COMPATIBILITY
       CREATE OR REPLACE VIEW is a PostgreSQL language extension. So is the
       concept of a temporary view. The WITH ( ... ) clause is an extension as
       well.

SEE ALSO
       ALTER VIEW (ALTER_VIEW(7)), DROP VIEW (DROP_VIEW(7)), CREATE
       MATERIALIZED VIEW (CREATE_MATERIALIZED_VIEW(7))

PostgreSQL 9.5.0		     2016			CREATE VIEW(7)
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