How to create view in hive

Last Updated: May 21, 2021 | Author: Michael-Chambers

Can we create a view in hive?

You can use Hive create view to create a virtual table based on the result-set of a complex SQL statement that may have multiple table joins. Apache Hive view is purely a logical construct (an alias for a complex query) with no physical data behind it. Note that, Hive view is different from lateral view.

How do you show view in hive?

There is nothing like SHOW VIEWS in Hive. DESCRIBE and DESCRIBE EXTENDED statements can be used for views like for tables, however, for DESCRIBE EXTENDED, the detailed table information has a variable named typeable which has value = ‘virtual view‘ for views. EXTERNAL and LOCATION clause also works for views.

What are the views in hive?

A view allows a query to be saved and treated like a table. It is a logical construct, as it does not store data like a table. In other words, materialized views are not currently supported by Hive. Logically, you can imagine that Hive executes the view and then uses the results in the rest of the query.

How do I create a partitioned view in hive?

Try this: hive> CREATE VIEW log_view PARTITIONED ON (pagename,year,month,day) AS SELECTuid,properties,pagename year,month,day FROM log; Reason: The column names used in the partition must be available at the end of view creation in the same order as mentioned in as partitions.

How do I create a partitioned view?

Steps to create a partitioned view
  1. Step 1 – Creating tables.
  2. Step 2 – Inserting Sample records.
  3. Step 3 – Creating view without check constraint.
  4. Step 4 – Filtering Data in the View.
  5. Step 5 – Adding Check Constraint in the table.
  6. Step 6 – Creating Partitioned view.
  7. Step 7 – Inserting values using partitioned view.

Can a materialized view be partitioned?

You can partition materialized views like you can partition tables. If joins back to tables or with other materialized views are necessary to retrieve the query result, then the rewritten query can take advantage of partition-wise joins.

Is materialized view updatable?

A materialized view contains a complete or partial copy of a table from a single point in time. Materialized views can be either read-only or updatable: Read-only materialized views provide read-only access to the table copy.

How do I edit a materialized view in Oracle?

Use the ALTER MATERIALIZED VIEW statement to modify an existing materialized view in one or more of the following ways:
  1. To change its storage characteristics.
  2. To change its refresh method, mode, or time.
  3. To alter its structure so that it is a different type of materialized view.
  4. To enable or disable query rewrite. Note:

Can we rename materialized view?

Parameters. Specifies the identifier of the materialized view to alter. This option allows you to rename a materialized view.

Can we replace materialized view?

No, you cannot alter the query of a materialized view without dropping it. The ALTER MATERIALIZED VIEW is used to modify an existing materialized view in one or more of the following ways: To change its storage characteristics. To change its refresh method, mode, or time.

Can we drop materialized view?

Use the DROP MATERIALIZED VIEW statement to remove an existing materialized view from the database. When you drop a materialized view, Oracle Database does not place it in the recycle bin. Therefore, you cannot subsequently either purge or undrop the materialized view.

Can we perform DML on materialized view?

Fast refresh for a materialized view containing only joins is possible after any type of DML to the base tables (direct-path or conventional INSERT , UPDATE , or DELETE ). If it is ON COMMIT , the refresh is performed at commit time of the transaction that does DML on the materialized view’s detail table.

What is the purpose of materialized view?

Oracle uses materialized views (also known as snapshots in prior releases) to replicate data to non-master sites in a replication environment and to cache expensive queries in a data warehouse environment.

What is difference between view and materialized view?

The basic difference between View and Materialized View is that Views are not stored physically on the disk. View can be defined as a virtual table created as a result of the query expression. However, Materialized View is a physical copy, picture or snapshot of the base table.

What is materialized view in Snowflake?

A materialized view is a pre-computed data set derived from a query specification (the SELECT in the view definition) and stored for later use. Because the data is pre-computed, querying a materialized view is faster than executing a query against the base table of the view.

What is materialized view with example?

In computing, a materialized view is a database object that contains the results of a query. For example, it may be a local copy of data located remotely, or may be a subset of the rows and/or columns of a table or join result, or may be a summary using an aggregate function.

Why materialized view is faster?

So here comes Materialized views helps us to get data faster. A table may need additional code to truncate/reload data. example: Materialized view having data from multiple tables can be setup to refresh automatically during non-peak hours. A physical table would need additional code to truncate/reload data.

What is faster join or subquery?

The advantage of a join includes that it executes faster. The retrieval time of the query using joins almost always will be faster than that of a subquery. By using joins, you can maximize the calculation burden on the database i.e., instead of multiple queries using one join query.

Can we create index on view?

The first index created on a view must be a unique clustered index. Creating a unique clustered index on a view improves query performance because the view is stored in the database in the same way a table with a clustered index is stored. The query optimizer may use indexed views to speed up the query execution.

How do you maintain materialized views?

For replication purposes, materialized views allow you to maintain copies of remote data on your local node.

REFRESH CLAUSE

  1. The refresh method used by Oracle to refresh data in materialized view.
  2. Whether the view is primary key based or row-id based.
  3. The time and interval at which the view is to be refreshed.

What privilege is required for materialized view?

The privileges required to create a materialized view should be granted directly rather than through a role. To create a materialized view in your own schema: You must have been granted the CREATE MATERIALIZED VIEW system privilege and either the CREATE TABLE or CREATE ANY TABLE system privilege.

Can we create primary key on materialized view?

WITH PRIMARY KEY is used to create a primary key materialized view i.e. the materialized view is based on the primary key of the master table instead of ROWID (for ROWID clause). PRIMARY KEY is the default option.

How do I make a materialized view read only?

  1. create materialized view mv_name. tablespace mv_data. as select * from base_table; By default materialized view refresh type is complete. This mv should be refreshed manually and using complete mode of refresh.
  2. create materialized view mv1. tablespace mv_data. build immediate. refresh fast.
  3. create materialized view mv1.

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