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Create View

CREATE VIEW [IF NOT EXISTS] [db_name.]view_name [(column_name [COMMENT column_comment], ...) ]
  [COMMENT view_comment]
  [TBLPROPERTIES (property_name = property_value, ...)]
  AS SELECT ...;

CREATE VIEW creates a view with the given name. An error is thrown if a table or view with the same name already exists. You can use IF NOT EXISTS to skip the error.

If no column names are supplied, the names of the view's columns will be derived automatically from the defining SELECT expression. (If the SELECT contains unaliased scalar expressions such as x+y, the resulting view column names will be generated in the form _C0, _C1, etc.) When renaming columns, column comments can also optionally be supplied. (Comments are not automatically inherited from underlying columns.)

A CREATE VIEW statement will fail if the view's defining SELECT expression is invalid.

Note that a view is a purely logical object with no associated storage. (No support for materialized views is currently available in Hive.) When a query references a view, the view's definition is evaluated in order to produce a set of rows for further processing by the query. (This is a conceptual description; in fact, as part of query optimization, Hive may combine the view's definition with the query's, e.g. pushing filters from the query down into the view.)

A view's schema is frozen at the time the view is created; subsequent changes to underlying tables (e.g. adding a column) will not be reflected in the view's schema. If an underlying table is dropped or changed in an incompatible fashion, subsequent attempts to query the invalid view will fail.

Views are read-only and may not be used as the target of LOAD/INSERT/ALTER. For changing metadata, see ALTER VIEW.

A view may contain ORDER BY and LIMIT clauses. If a referencing query also contains these clauses, the query-level clauses are evaluated after the view clauses (and after any other operations in the query). For example, if a view specifies LIMIT 5, and a referencing query is executed as (select * from v LIMIT 10), then at most 5 rows will be returned.

Starting with Hive 0.13.0, the view's select statement can include one or more common table expressions (CTEs) as shown in the SELECT syntax. For examples of CTEs in CREATE VIEW statements, see Common Table Expression.

Example of view creation:

CREATE VIEW onion_referrers(url COMMENT 'URL of Referring page')
  COMMENT 'Referrers to The Onion website'
  AS
  SELECT DISTINCT referrer_url
  FROM page_view
  WHERE page_url='http://www.theonion.com';

Use SHOW CREATE TABLE to display the CREATE VIEW statement that created a view.

Drop View

DROP VIEW [IF EXISTS] view_name;

DROP VIEW removes metadata for the specified view. (It is illegal to use DROP TABLE on a view.)

When dropping a view referenced by other views, no warning is given (the dependent views are left dangling as invalid and must be dropped or recreated by the user).

In Hive 0.7.0 or later, DROP returns an error if the view doesn't exist, unless IF EXISTS is specified or the configuration variable hive.exec.drop.ignorenonexistent is set to true.

Example:

DROP VIEW onion_referrers;

Alter View Properties

ALTER VIEW view_name SET TBLPROPERTIES table_properties;

table_properties:
  : (property_name = property_value, property_name = property_value, ...)

As with ALTER TABLE, you can use this statement to add your own metadata to a view.

Alter View As Select

ALTER VIEW view_name AS select_statement;

Alter View As Select changes the definition of a view, which must exist. The syntax is similar to that for CREATE VIEW and the effect is the same as for CREATE OR REPLACE VIEW.

Note: The view must already exist, and if the view has partitions, it could not be replaced by Alter View As Select.