What is the difference between Views and Materialized Views in Oracle?

aterialized views are disk based and update periodically base upon the query definition.

Views are virtual only and run the query definition each time they are accessed.

Views evaluate the data in the tables underlying the view definition at the time the view is queried. It is a logical view of your tables, with no data stored anywhere else. The upside of a view is that it will always return the latest data to you. The downside of a view is that its performance depends on how good a select statement the view is based on. If the select statement used by the view joins many tables, or uses joins based on non-indexed columns, the view could perform poorly.

Materialized views are similar to regular views, in that they are a logical view of your data (based on a select statement), however, the underlying query resultset has been saved to a table. The upside of this is that when you query a materialized view, you are querying a table, which may also be indexed. In addition, because all the joins have been resolved at materialized view refresh time, you pay the price of the join once (or as often as you refresh your materialized view), rather than each time you select from the materialized view. In addition, with query rewrite enabled, Oracle can optimize a query that selects from the source of your materialized view in such a way that it instead reads from your materialized view. In situations where you create materialized views as forms of aggregate tables, or as copies of frequently executed queries, this can greatly speed up the response time of your end user application. The downside though is that the data you get back from the materialized view is only as up to date as the last time the materialized view has been refreshed.

Materialized views can be set to refresh manually, on a set schedule, or based on the database detecting a change in data from one of the underlying tables. Materialized views can be incrementally updated by combining them with materialized view logs, which act as change data capture sources on the underlying tables.

Materialized views are most often used in data warehousing / business intelligence applications where querying large fact tables with thousands of millions of rows would result in query response times that resulted in an unusable application.

Difference between View and Materialized view is one of the popular SQL interview question, much like truncate vs delete, correlated vs noncorrelated subquery or primary key vs unique key.  This is one of the classic question which keeps appearing in SQL interview now and then and you simply can’t afford not to learn about them. Doesn’t matter if you are a programmer, developer or DBA, this SQL questions is common to all. Views are concept which not every programmer familiar of, it simply not in the category of CRUD operation or database transactions or SELECT query, its little advanced concept for average programmer. Views allows a level of separation than original table in terms of access rights but it always fetch updated data. Let’s see What is View in database, What is materialized View and difference between view and materialized view in database.

What is View in database

Views are logical virtual table created by “select query” but the result is not stored anywhere in the disk and every time we need to fire the query when we need data, so always we get updated or latest data from original tables. Performance of the view depend upon our select query. If we want to improve the performance of view we should avoid to use join statement in our query or if we need multiple joins between table always try to use index based column for joining as we know index based columns are faster than non index based column. View allow to store definition of the query in the database itself.

 

What is Materialized View in database

Materialized views are also logical view of our data driven by select query but the result of the query will get stored in the table or disk, also definition of the query will also store in the database .When we see the performance of Materialized view it is better than normal View because the data of materialized view will stored in table and table may be indexed so faster for joining also joining is done at the time of materialized views refresh time so no need to every time fire join statement as in case of view.

Difference between View vs Materialized View in database

Based upon on our understanding of View and Materialized View, Let’s see, some short difference between them :

 

1) First difference between View and materialized view is that, In Views query result is not stored in the disk or database but Materialized view allow to store query result in disk or table.

 

2) Another difference between View vs materialized view is that, when we create view using any table,  rowid of view is same as original table but in case of Materialized view rowid is different.

 

3) One more difference between View and materialized view in database is that, In case of View we always get latest data but in case of Materialized view we need to refresh the view for getting latest data.

 

4) Performance of View is less than Materialized view.

 

5) This is continuation of first difference between View and Materialized View, In case of view its only the logical view of table no separate copy of table but in case of Materialized view we get physically separate copy of table

 

6) Last difference between View vs Materialized View is that, In case of Materialized view we need extra trigger or some automatic method so that we can keep MV refreshed, this is not required for views in database.

 

When to Use View vs Materialized View in SQL

Mostly in application we use views because they are more feasible,  only logical representation of table data no extra space needed. We easily get replica of data and we can perform our operation on that data without affecting actual table data but when we see performance which is crucial for large application they use materialized view where Query Response time matters so Materialized views are used mostly with data ware housing or business intelligence application.

 

That’s all on difference between View and materialized View in database or SQL. I suggest always prepare this question in good detail and if you can get some hands on practice like creating Views, getting data from Views then try that as well.