Create/Drop/Alter View

Create View

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:

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

Drop View

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:

Alter View Properties

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

Alter View As Select

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.

Create/Drop/Alter Index

This section provides a brief introduction to Hive indexes, which are documented more fully here:

• Overview of Hive Indexes
• Indexes design document

In Hive 0.12.0 and earlier releases, the index name is case-sensitive for CREATE INDEX and DROP INDEX statements. However, ALTER INDEX requires an index name that was created with lowercase letters (see HIVE-2752). This bug is fixed in Hive 0.13.0 by making index names case-insensitive for all HiveQL statements. For releases prior to 0.13.0, the best practice is to use lowercase letters for all index names.

Create Index

CREATE INDEX creates an index on a table using the given list of columns as keys. See CREATE INDEX in the Indexes design document.

Drop Index

DROP INDEX drops the index, as well as deleting the index table.

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

Alter Index

ALTER INDEX ... REBUILD builds an index that was created using the WITH DEFERRED REBUILD clause, or rebuilds a previously built index. If PARTITION is specified, only that partition is rebuilt.

Create/Drop Function

Temporary Functions

Create Temporary Function

This statement lets you create a function that is implemented by the class_name. You can use this function in Hive queries as long as the session lasts. You can use any class that is in the class path of Hive. You can add jars to class path by executing 'ADD JAR' statements. Please refer to the CLI section Hive Interactive Shell Commands, including Hive Resources, for more information on how to add/delete files from the Hive classpath. Using this, you can register User Defined Functions (UDF's).

Also see Hive Plugins for general information about creating custom UDFs.

Drop Temporary Function

You can unregister a UDF as follows:

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

Permanent Functions

In Hive 0.13 or later, functions can be registered to the metastore, so they can be referenced in a query without having to create a temporary function each session.

Create Function

This statement lets you create a function that is implemented by the class_name. Jars, files, or archives which need to be added to the environment can be specified with the USING clause; when the function is referenced for the first time by a Hive session, these resources will be added to the environment as if ADD JAR/FILE had been issued. If Hive is not in local mode, then the resource location must be a non-local URI such as an HDFS location.

The function will be added to the database specified, or to the current database at the time that the function was created. The function can be referenced by fully qualifying the function name (db_name.funciton_name), or can be referenced without qualification if the function is in the current database.

Drop Function

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