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CREATE VIEW

   CREATE VIEW — define a new view

Synopsis

CREATE [ OR REPLACE ] [ TEMP | TEMPORARY ] [ RECURSIVE ] VIEW name [ ( column_na
me [, ...] ) ]
    [ 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
   relation (table, sequence, index, view, materialized view, 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 (enum)
                This parameter may be either local or cascaded, and is
                equivalent to specifying WITH [ CASCADED | LOCAL ] CHECK
                OPTION (see below).

        security_barrier (boolean)
                This should be used if the view is intended to provide
                row-level security. See Section 39.5 for full details.

        security_invoker (boolean)
                This option causes the underlying base relations to be
                checked against the privileges of the user of the view
                rather than the view owner. See the notes below for full
                details.

          All of the above options can be changed on existing views using
          ALTER VIEW.

   query
          A SELECT or VALUES 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, UPDATE, and MERGE
          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, UPDATE, and MERGE 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. MERGE is not supported if the view or any of its base
          relations have rules.

Notes

   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 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;

   By default, access to the underlying base relations referenced in the
   view is determined by the 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 for details.

   If the view has the security_invoker property set to true, access to
   the underlying base relations is determined by the permissions of the
   user executing the query, rather than the view owner. Thus, the user of
   a security invoker view must have the relevant permissions on the view
   and its underlying base relations.

   If any of the underlying base relations is a security invoker view, it
   will be treated as if it had been accessed directly from the original
   query. Thus, a security invoker view will always check its underlying
   base relations using the permissions of the current user, even if it is
   accessed from a view without the security_invoker property.

   If any of the underlying base relations has row-level security enabled,
   then by default, the row-level security policies of the view owner are
   applied, and access to any additional relations referred to by those
   policies is determined by the permissions of the view owner. However,
   if the view has security_invoker set to true, then the policies and
   permissions of the invoking user are used instead, as if the base
   relations had been referenced directly from the query using the view.

   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.
   Functions in the view are executed with the privileges of the user
   executing the query or the function owner, depending on whether the
   functions are defined as SECURITY INVOKER or SECURITY DEFINER. Thus,
   for example, calling CURRENT_USER directly in a view will always return
   the invoking user, not the view owner. This is not affected by the
   view's security_invoker setting, and so a view with security_invoker
   set to false is not equivalent to a SECURITY DEFINER function and those
   concepts should not be confused.

   The user creating or replacing a view must have USAGE privileges on any
   schemas referred to in the view query, in order to look up the
   referenced objects in those schemas. Note, however, that this lookup
   only happens when the view is created or replaced. Therefore, the user
   of the view only requires the USAGE privilege on the schema containing
   the view, not on the schemas referred to in the view query, even for a
   security invoker view.

   When CREATE OR REPLACE VIEW is used on an existing view, only the
   view's defining SELECT rule, plus any WITH ( ... ) parameters and its
   CHECK OPTION are 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, DELETE, and MERGE 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, UPDATE, or MERGE statement attempts to assign a value to it.

   If the view is automatically updatable the system will convert any
   INSERT, UPDATE, DELETE, or MERGE 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, DELETE, and MERGE statements on the view. However,
   an UPDATE or MERGE 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 or MERGE 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, UPDATE, and MERGE 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 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,
   DELETE, or MERGE 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. Another possibility is
   to create rules (see CREATE RULE), but in practice triggers are easier
   to understand and use correctly. Also note that MERGE is not supported
   on relations with rules.

   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, by default, the view's owner must have the relevant
   privileges on the underlying base relations, whereas the user
   performing the update does not need any permissions on the underlying
   base relations (see Section 39.5). However, if the view has
   security_invoker set to true, the user performing the update, rather
   than the view owner, must have the relevant privileges on the
   underlying base relations.

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, as are security barrier views and security invoker views.

See Also

   ALTER VIEW, DROP VIEW, CREATE MATERIALIZED VIEW