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on views. This technique allows the definition of other logic for execution in place of an insert, update, or delete operation on the views. Thus database systems can implement data modifications based on read-only views. However, an INSTEAD OF trigger does not change the read-only or updatable
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in a base table lack any defined ordering, rows available through a view do not appear with any default sorting. A view is a relational table, and the relational model defines a table as a set of rows. Since sets are not ordered — by definition — neither are the rows of a view.
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Views can represent a subset of the data contained in a table. Consequently, a view can limit the degree of exposure of the underlying tables to the outer world: a given user may have permission to query the view, while denied access to the rest of the base
249:) does not allow an ORDER BY clause in the subquery of a CREATE VIEW command, just as it is refused in a CREATE TABLE statement. However, sorted data can be obtained from a view, in the same way as any other table — as part of a query
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The optimizer then removes unnecessary fields and complexity (for example it is not necessary to read the address, since the parent invocation does not make use of it) and then sends the query to the SQL engine for processing.
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operations can be performed on updatable views. Read-only views do not support such operations because the DBMS cannot map the changes to the underlying base tables. A view update is done by key preservation.
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Views can be defined as read-only or updatable. If the database system can determine the reverse mapping from the view schema to the schema of the underlying base tables, then the view is updatable.
316:. They give a static snapshot of the data and may include data from remote sources. The accuracy of a materialized view depends on the frequency of trigger mechanisms behind its updates.
225:, so can a database view. In another parallel with functions, database users can manipulate nested views, thus one view can aggregate data from other views. Without the use of views, the
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A view is equivalent to its source query. When queries are run against views, the query is modified. For example, if there exists a view named accounts_view with the content as follows:
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Views take very little space to store; the database contains only the definition of a view, not a copy of all the data that it presents.
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introduced in its 2000 version indexed views which only store a separate index from the table, but not the entire data.
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Views can hide the complexity of data. For example, a view could appear as Sales2020 or Sales2021, transparently
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that presents a limited perspective of the database to a user. This pre-established query command is kept in the
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The RDBMS then takes the simple query, replaces the equivalent view, then sends the following to the
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would become much more difficult. Views can make it easier to create lossless join decomposition.
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Views are stored queries that when invoked produce a result set. A view acts as a virtual table.
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Views structure data in a way that classes of users find natural and intuitive.
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provides so-called "materialized query tables" (MQTs) for the same purpose.
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are reflected in the data shown in subsequent invocations of the view.
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clause in the view definition is meaningless; the SQL standard (
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and simplify multiple tables into a single virtual table.
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then the application could run a simple query such as:
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335:implemented materialized views in its 9.3 release.
312:: pre-executed, non-virtual views commonly used in
60:. Unsourced material may be challenged and removed.
304:have extended the views from read-only subsets of
281:Some systems support the definition of INSTEAD OF
257:) do not abide by this SQL standard restriction.
253:on that view. Nevertheless, some DBMS (such as
188:Views can act as aggregated tables, where the
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1178:Groff, James R.; Weinberg, Paul N. (1999).
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173:Views can provide advantages over tables:
1187:. Osborne/McGraw-Hill. pp. 291–292.
120:Learn how and when to remove this message
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319:Materialized views were introduced by
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58:adding citations to reliable sources
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162:, a view does not form part of the
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27:Database stored query result set
1152:from the original on 2023-11-23
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45:needs additional citations for
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286:property of the view itself.
261:Read-only vs. updatable views
221:(in programming) can provide
207:the actual underlying table.
1215:Database management systems
1181:SQL: The Complete Reference
664:Database management systems
302:database management systems
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1070:Object–relational database
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1045:Federated database system
778:Blockchain-based database
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1148:. Oracle. 2023-12-12.
1075:Transaction processing
1030:Database normalization
973:Query rewriting system
492:-- Preprocessed query:
1050:Referential integrity
294:Further information:
1040:Distributed database
628:Bidirectionalization
329:Microsoft SQL Server
54:improve this article
1060:Relational calculus
938:Concurrency control
229:of databases above
160:relational database
1142:"25.5 Using Views"
1055:Relational algebra
999:Query optimization
804:Armstrong's axioms
495:------------------
310:materialized views
290:Materialized views
231:second normal form
152:. Unlike ordinary
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729:Wide-column store
724:Document-oriented
348:-- accounts_view:
296:Materialized view
192:aggregates data (
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16:(Redirected from
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457:-- Simple query
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321:Oracle Database
308:, particularly
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255:Oracle Database
190:database engine
164:physical schema
150:data dictionary
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69:"View" SQL
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241:Therefore, an
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829:Candidate key
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478:accounts_view
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351:-------------
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110:December 2023
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71: –
70:
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65:Find sources:
59:
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49:
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43:This article
41:
37:
32:
31:
19:
18:Database view
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1154:. Retrieved
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460:------------
451:
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235:
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205:partitioning
172:
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144:of a stored
137:
131:
116:
107:
97:
90:
83:
76:
64:
52:Please help
47:verification
44:
1113:WikiProject
1004:Replication
892:Transaction
834:Foreign key
814:CAP theorem
761:Multi-model
609:customer_id
597:customer_id
447:customer_id
435:customer_id
339:Equivalence
223:abstraction
155:base tables
1209:Categories
1194:0072118458
1156:2023-12-12
1125:References
978:Query plan
931:Components
849:Unique key
766:comparison
700:comparison
690:Relational
683:comparison
546:money_sent
531:money_sent
384:money_sent
369:money_sent
333:PostgreSQL
217:Just as a
181:Views can
142:result set
80:newspapers
987:Functions
922:Partition
749:In-memory
707:Key–value
251:statement
1150:Archived
1093:Category
1009:Sharding
865:Relation
839:Superkey
794:Database
787:Concepts
622:See also
323:, while
300:Various
283:triggers
247:SQL:2003
243:ORDER BY
236:Just as
219:function
134:database
1103:Outline
902:Trigger
858:Objects
561:address
555:balance
507:balance
472:balance
399:address
393:balance
325:IBM Db2
198:average
140:is the
94:scholar
1191:
917:Cursor
875:column
744:NewSQL
516:SELECT
498:SELECT
463:SELECT
354:SELECT
275:DELETE
273:, and
271:UPDATE
267:INSERT
178:table.
96:
89:
82:
75:
67:
1185:(PDF)
1146:MySQL
907:Index
870:table
773:Cloud
739:NoSQL
734:Graph
671:Types
158:in a
146:query
132:In a
101:JSTOR
87:books
1189:ISBN
958:ODBC
948:JDBC
887:View
824:Null
819:CRUD
799:ACID
754:list
717:list
695:list
579:JOIN
570:FROM
519:name
510:FROM
501:name
475:FROM
466:name
417:JOIN
408:FROM
357:name
306:data
238:rows
183:join
138:view
136:, a
73:news
1220:SQL
953:XQJ
880:row
567:...
405:...
194:sum
56:by
1211::
1168:^
1159:.
1144:.
1133:^
588:ON
552:AS
487::
426:ON
390:AS
269:,
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1197:.
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