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CREATE VIEW(7) PostgreSQL 12.18 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 40.5 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 because the column name defaults to ?column?; also, the column data type
defaults to text, which might not be what you wanted. Better style for a string literal in
a view's result is 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 40.5 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 40.5 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 40.5).
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 12.18 2024 CREATE VIEW(7)
Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
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Under GNU General Public License
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