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:

       •   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 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))