HOME

TheInfoList



OR:

In
computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes, and development of both hardware and software. Computing has scientific, e ...
, a materialized view is a
database In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases sp ...
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 Join may refer to: * Join (law), to include additional counts or additional defendants on an indictment *In mathematics: ** Join (mathematics), a least upper bound of sets orders in lattice theory ** Join (topology), an operation combining two top ...
result, or may be a summary using an
aggregate function In database management, an aggregate function or aggregation function is a function where the values of multiple rows are grouped together to form a single summary value. Common aggregate functions include: * Average (i.e., arithmetic mean) * ...
. The process of setting up a materialized view is sometimes called materialization.Compare: This is a form of caching the results of a query, similar to memoization of the value of a function in functional languages, and it is sometimes described as a form of
precomputation In algorithms, precomputation is the act of performing an initial computation before run time to generate a lookup table that can be used by an algorithm to avoid repeated computation each time it is executed. Precomputation is often used in al ...
. As with other forms of precomputation, database users typically use materialized views for performance reasons, i.e. as a form of optimization. Materialized views which store data based on remote tables were also known as
snapshot Snapshot, snapshots or snap shot may refer to: * Snapshot (photography), a photograph taken without preparation Computing * Snapshot (computer storage), the state of a system at a particular point in time * Snapshot (file format) or SNP, a file ...
s (deprecated Oracle terminology). In any database management system following the relational model, a view is a virtual
table Table may refer to: * Table (furniture), a piece of furniture with a flat surface and one or more legs * Table (landform), a flat area of land * Table (information), a data arrangement with rows and columns * Table (database), how the table data ...
representing the result of a
database In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases sp ...
query. Whenever a query or an update addresses an ordinary view's virtual table, the DBMS converts these into queries or updates against the underlying base tables. A materialized view takes a different approach: the query result is cached as a concrete ("materialized") table (rather than a view as such) that may be updated from the original base tables from time to time. This enables much more efficient access, at the cost of extra storage and of some data being potentially out-of-date. Materialized views find use especially in
data warehousing In computing, a data warehouse (DW or DWH), also known as an enterprise data warehouse (EDW), is a system used for reporting and data analysis and is considered a core component of business intelligence. DWs are central repositories of integra ...
scenarios, where frequent queries of the actual base tables can be expensive. In a materialized view,
indexes Index (or its plural form indices) may refer to: Arts, entertainment, and media Fictional entities * Index (''A Certain Magical Index''), a character in the light novel series ''A Certain Magical Index'' * The Index, an item on a Halo megastru ...
can be built on any column. In contrast, in a normal view, it's typically only possible to exploit indexes on columns that come directly from (or have a mapping to) indexed columns in the base tables; often this functionality is not offered at all.


Implementations


Oracle

Materialized views were implemented first by the Oracle Database: the Query rewrite feature was added from version 8i. Example syntax to create a materialized view in Oracle: CREATE MATERIALIZED VIEW MV_MY_VIEW REFRESH FAST START WITH SYSDATE NEXT SYSDATE + 1 AS SELECT * FROM ;


PostgreSQL

In
PostgreSQL PostgreSQL (, ), also known as Postgres, is a free and open-source relational database management system (RDBMS) emphasizing extensibility and SQL compliance. It was originally named POSTGRES, referring to its origins as a successor to the In ...
, version 9.3 and newer natively support materialized views. In version 9.3, a materialized view is not auto-refreshed, and is populated only at time of creation (unless WITH NO DATA is used). It may be refreshed later manually using REFRESH MATERIALIZED VIEW. In version 9.4, the refresh may be concurrent with selects on the materialized view if CONCURRENTLY is used. Example syntax to create a materialized view in PostgreSQL: CREATE MATERIALIZED VIEW MV_MY_VIEW WITH_(storage_parameter_[=_value[,_..._.html" ;"title="_value.html" ;"title="WITH (storage_parameter [= value">WITH (storage_parameter [= value[, ... ">_value.html" ;"title="WITH (storage_parameter [= value">WITH (storage_parameter [= value[, ... ] [ TABLESPACE tablespace_name ] AS SELECT * FROM ;


SQL Server

Microsoft SQL Server differs from other RDBMS by the way of implementing materialized view via a concept known as "Indexed Views". The main difference is that such views do not require a refresh because they are in fact always synchronized to the original data of the tables that compound the view. To achieve this, it is necessary that the lines of origin and destination are "deterministic" in their mapping which limits the types of possible queries to do this. This mechanism has been realised since the 2000 version of SQL Server. Example syntax to create a materialized view in SQL Server: CREATE VIEW MV_MY_VIEW WITH SCHEMABINDING AS SELECT COL1, SUM(COL2) AS TOTAL FROM GROUP BY COL1; GO CREATE UNIQUE CLUSTERED INDEX XV ON MV_MY_VIEW (COL1);


Stream processing frameworks

Apache Kafka (since v0.10.2), Apache Spark (since v2.0), Apache Flink, Materialize, and RisingWave all support materialized views on streams of data.


Others

Materialized views are also supported in Sybase SQL Anywhere. In
IBM Db2 Db2 is a family of data management products, including database servers, developed by IBM. It initially supported the relational model, but was extended to support object–relational features and non-relational structures like JSON a ...
, they are called "materialized query tables".
ClickHouse ClickHouse is an open-source column-oriented DBMS (columnar database management system) for online analytical processing (OLAP) that allows users to generate analytical reports using SQL queries in real-time. ClickHouse Inc. is headquartered in ...
supports materialized views that automatically refresh on merges.
MySQL MySQL () is an open-source relational database management system (RDBMS). Its name is a combination of "My", the name of co-founder Michael Widenius's daughter My, and "SQL", the acronym for Structured Query Language. A relational database o ...
doesn't support materialized views natively, but workarounds can be implemented by using triggers or stored procedures or by using the open-source application Flexviews. Materialized views can be implemented in
Amazon DynamoDB Amazon DynamoDB is a fully managed proprietary NoSQL database service that supports key–value and document data structures and is offered by Amazon.com as part of the Amazon Web Services portfolio. DynamoDB exposes a similar data model to and ...
using data modification events captured by DynamoDB Streams. Google announced in 8 April 2020 the availability of materialized views for BigQueryGoogle BigQuery Materialized Views documentation
Google.com Retrieved on 2020-05-20. as a beta release.


References


External links



* ttp://download.oracle.com/docs/cd/B10501_01/server.920/a96568/rarmviea.htm#94135 Oracle9i Replication Management API Reference Release 2 (9.2)br>Materialized Views in Oracle 11.2Creating Materialized Views In MySQL
{{Databases Relational model Data modeling Database management systems Databases Articles with example SQL code