CREATE VIEW(7) PostgreSQL 9.6.6 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 [ schema . ] view_name (column_names) AS SELECT ...;
is equivalent to
CREATE VIEW [ schema . ] view_name AS WITH RECURSIVE view_name (column_names) AS (SELECT ...) SELECT column_names FROM view_name;
A view column name 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 39.5, "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 39.5, "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:
o The view must have exactly one entry in its FROM list, which must
be a table or another updatable view.
o The view definition must not contain WITH, DISTINCT, GROUP BY,
HAVING, LIMIT, or OFFSET clauses at the top level.
o The view definition must not contain set operations (UNION,
INTERSECT or EXCEPT) at the top level.
o 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
39.5, "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
39.5, "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 public.nums_1_100 (n) AS
VALUES (1)
UNION ALL
SELECT n+1 FROM nums_1_100 WHERE n < 100;
Notice that although the recursive view's name is schema-qualified in
this CREATE, its internal self-reference is not schema-qualified. This
is because the implicitly-created CTE's name cannot be
schema-qualified.
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 9.6.6 2017 CREATE VIEW(7)
PostgreSQL 9.6.6 - Generated Sat Dec 2 07:53:46 CST 2017