CREATE VIEW

Description

Views are based on the result-set of an SQL query. CREATE VIEW constructs a virtual table that has no physical data therefore other operations like ALTER VIEW and DROP VIEW only change metadata.

Syntax

CREATE [ OR REPLACE ] [ [ GLOBAL ] TEMPORARY ] VIEW [ IF NOT EXISTS ] view_identifier
    create_view_clauses AS query

Parameters

OR REPLACE

If a view of same name already exists, it will be replaced.
[ GLOBAL ] TEMPORARY

TEMPORARY views are session-scoped and are dropped when the session ends; no entry is persisted in the underlying metastore. Temporary views live in the per-session system.session namespace.

GLOBAL TEMPORARY views are tied to the system-preserved temporary database global_temp.
IF NOT EXISTS

Creates a view if it does not exist. This clause is not supported for TEMPORARY views yet.
view_identifier

Specifies a view name.
- For a persistent view the name may be optionally qualified with a database name (or a catalog and database). If the name is not qualified the view is created in the current schema.
  
  Syntax: [ catalog_name. ] [ database_name. ] view_name
- For a temporary view the name may be optionally qualified with the session schema (session or system.session). Any other qualifier is rejected with INVALID_TEMP_OBJ_QUALIFIER. For example, CREATE TEMPORARY VIEW session.v ... and CREATE TEMPORARY VIEW system.session.v ... are accepted; CREATE TEMPORARY VIEW mydb.v ... is not.
  
  Syntax: [ { session | system.session } . ] view_name
The fully qualified view name must be unique within its schema.
create_view_clauses

These clauses are optional and order insensitive. It can be of following formats.
- [ ( column_name [ COMMENT column_comment ], ... ) ] to specify column-level comments.
- [ COMMENT view_comment ] to specify view-level comments.
- [ TBLPROPERTIES ( property_name = property_value [ , ... ] ) ] to add metadata key-value pairs.
- [ WITH SCHEMA { BINDING | COMPENSATION | [ TYPE ] EVOLUTION } ] to specify how the view reacts to schema changes
  
  This clause is not supported for TEMPORARY views.
  - BINDING - The view can tolerate only type changes in the underlying schema requiring safe up-casts.
  - COMPENSATION - The view can tolerate type changes in the underlying schema requiring casts. Runtime casting errors may occur.
  - TYPE EVOLUTION - The view will adapt to any type changes in the underlying schema.
  - EVOLUTION - For views defined without a column lists any schema changes are adapted by the view, including, for queries with SELECT * dropped or added columns. If the view is defined with a column list, the clause is interpreted as TYPE EVOLUTION.
  The default is WITH SCHEMA COMPENSATION.
query

A SELECT statement that constructs the view from base tables or other views.

A persistent view cannot reference temporary views, temporary functions, or session variables.

For a persistent view, the SQL Path in effect at CREATE VIEW time is captured into the view’s metadata; the body resolves against that frozen path on every reference, not the invoker’s current path. Use DESCRIBE EXTENDED to inspect the captured path. See SET PATH.

Examples

-- Create or replace view for `experienced_employee` with comments.
CREATE OR REPLACE VIEW experienced_employee
    (ID COMMENT 'Unique identification number', Name) 
    COMMENT 'View for experienced employees'
    AS SELECT id, name FROM all_employee
        WHERE working_years > 5;

-- Create a global temporary view `subscribed_movies`.
CREATE GLOBAL TEMPORARY VIEW subscribed_movies 
    AS SELECT mo.member_id, mb.full_name, mo.movie_title
        FROM movies AS mo INNER JOIN members AS mb 
        ON mo.member_id = mb.id;

-- Create a view filtering the `orders` table which will adjust to schema changes in `orders`.
CREATE OR REPLACE VIEW open_orders WITH SCHEMA EVOLUTION
    AS SELECT * FROM orders WHERE status = 'open';

Create a temporary view with a session qualifier

-- Unqualified, `session`-qualified, and `system.session`-qualified names all create the same
-- temporary view in the per-session `system.session` namespace.
CREATE TEMPORARY VIEW recent_orders
    AS SELECT * FROM orders WHERE order_date > current_date - INTERVAL 7 DAYS;

CREATE OR REPLACE TEMPORARY VIEW session.recent_orders
    AS SELECT * FROM orders WHERE order_date > current_date - INTERVAL 7 DAYS;

CREATE OR REPLACE TEMPORARY VIEW system.session.recent_orders
    AS SELECT * FROM orders WHERE order_date > current_date - INTERVAL 7 DAYS;

-- All three names address the same temporary view:
SELECT count(*) FROM recent_orders;
SELECT count(*) FROM session.recent_orders;
SELECT count(*) FROM system.session.recent_orders;

-- DROP VIEW accepts the same qualifiers (there is no DROP TEMPORARY VIEW form):
DROP VIEW session.recent_orders;

-- Any other qualifier on a TEMPORARY view is rejected.
CREATE TEMPORARY VIEW mydb.bad_temp AS SELECT 1;
  [INVALID_TEMP_OBJ_QUALIFIER] qualifier `mydb` is not allowed for temporary VIEW ...

CREATE TEMPORARY VIEW system.builtin.bad_temp AS SELECT 1;
  [INVALID_TEMP_OBJ_QUALIFIER] qualifier `system`.`builtin` is not allowed for temporary VIEW ...

Frozen SQL Path

A persistent view captures the SQL Path that is in effect at CREATE VIEW time. The view body resolves against that frozen path on every reference, even when the caller’s session has set a different PATH. See SET PATH.

> CREATE SCHEMA views_a;
> CREATE SCHEMA views_b;
> CREATE TABLE views_a.t USING parquet AS SELECT 1 AS id;
> CREATE TABLE views_b.t USING parquet AS SELECT 2 AS id;

-- The PATH at CREATE VIEW time points at views_a, so unqualified `t` in the view body binds to
-- views_a.t.
> SET PATH = spark_catalog.views_a, system.builtin;
> CREATE VIEW default.v_frozen AS SELECT id FROM t;

-- Flip the live PATH. The view body still resolves `t` against the frozen path.
> SET PATH = spark_catalog.views_b, system.builtin;

-- A bare query follows the LIVE path:
> SELECT id FROM t;
 2

-- The view body follows its FROZEN path:
> SELECT id FROM default.v_frozen;
 1

-- DESCRIBE EXTENDED shows the captured path:
> DESCRIBE EXTENDED default.v_frozen;
 ...
 SQL Path  spark_catalog.views_a, system.builtin

Spark SQL Guide