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Results for query rewrite


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Database Concepts

Partitions, Views, and Other Schema Objects

Query RewriteQuery rewrite is an optimization technique that transforms a user request written in terms of … . Because materialized views contain precomputed aggregates and joins, query rewrite can quickly answer … in the SQL statement. Because query rewrite is transparent, materialized views can

Database Data Warehousing Guide

Basic Materialized Views

Query Rewrite RestrictionsQuery rewrite is not possible with all materialized views. If query rewrite is not occurring when … for rewrite. If this shows that not all types of query rewrite are possible, use the procedure … DBMS_ADVISOR.TUNE_MVIEW to see if the materialized view can be defined

Database Data Warehousing Guide

Basic Query Rewrite

Controlling Query RewriteA materialized view is only eligible for query rewrite if the ENABLE QUERY REWRITE clause has been … , ALTER SESSION can be used to disable or enable query rewrite for that session only. An example is … the following: ALTER SESSION SET QUERY_REWRITE_ENABLED = TRUE; You can set the level

Database Data Warehousing Guide

Advanced Query Rewrite

Query Rewrite Using Dimensions… Figure 19-2 Query Rewrite Subgraphs Description of \"Figure 19-2 Query Rewrite Subgraphs\" Common … rewrite, the materialized view is joined to the appropriate tables in the query delta. For example … rewrite the query if this join is lossless

Database Data Warehousing Guide

Advanced Query Rewrite

Other Query Rewrite ConsiderationsThe following discusses some of the other cases when query rewrite is possible: Query Rewrite Using … Nested Materialized Views Query Rewrite in the Presence of Inline Views Query Rewrite Using Remote … Tables Query Rewrite

Database Data Warehousing Guide

Advanced Query Rewrite

General Query Rewrite MethodsThe optimizer has a number of different types of query rewrite methods that it can choose from to … answer a query. When text match rewrite is not possible, this group of rewrite methods is known as … general query rewrite. The advantage of using these more advanced

Database Data Warehousing Guide

Advanced Query Rewrite

Query Rewrite Considerations: Statisticsthe materialized view and the tables in the query to make a cost-based choice. Materialized views

Database Data Warehousing Guide

Basic Query Rewrite

Accuracy of Query RewriteQuery rewrite offers three levels of rewrite integrity that are controlled by the session parameter … relationships specified using dimensions. This mode offers greater query rewrite capabilities but also creates … contain stale data as well as those that contain fresh data. This mode offers the maximum

Database Data Warehousing Guide

Advanced Query Rewrite

Query Rewrite Considerations: DimensionsQUERY_REWRITE_INTEGRITY to TRUSTED or STALE_TOLERATED for query rewrite to take advantage of the relationships declared in dimensions.

Database Data Warehousing Guide

Basic Query Rewrite

Overview of Query RewriteDatabase employs an extremely powerful process called query rewrite to quickly answer the query using … ability to take advantage of query rewrite, which transforms a SQL statement expressed in terms of … intervention and no reference to the materialized view in the SQL statement. Because query

Database Data Warehousing Guide

Advanced Query Rewrite

Query Rewrite Considerations: HintsYou can include hints in the SELECT blocks of your SQL statements to control whether query rewrite … occurs. Using the NOREWRITE hint in a query prevents the optimizer from rewriting it. The REWRITE hint … with no argument in a query forces the optimizer to use a materialized view (if any) to rewrite

Database Data Warehousing Guide

Advanced Query Rewrite

Query Rewrite Considerations: ConstraintsMake sure all inner joins referred to in a materialized view have referential integrity (foreign key/primary key constraints) with additional NOT NULL constraints on the foreign key columns. Since constraints tend to impose a large overhead, you could make them NO VALIDATE and RELY and set the parameter QUERY_REWRITE_INTEGRITY to STALE_TOLERATED or TRUSTED. However, if you set QUERY_REWRITE_INTEGRITY

Database Data Warehousing Guide

Advanced Query Rewrite

Query Rewrite Considerations: AggregatesTo get the maximum benefit from query rewrite, make sure that all aggregates which are needed to … aggregates are quite similar to those for incremental refresh. For instance, if AVG(x) is in the query

Database Data Warehousing Guide

Advanced Query Rewrite

19 Advanced Query RewriteThis chapter discusses advanced query rewrite topics in Oracle, and contains: How Oracle Rewrites … Queries Types of Query Rewrite Other Query Rewrite Considerations Advanced Query Rewrite Using … Equivalences Creating Result Cache Materialized Views

Database Data Warehousing Guide

Basic Materialized Views

Enabling Query RewriteBefore creating a materialized view, you can verify what types of query rewrite are possible by … materialized view so that many types of query rewrite are possible. Once the materialized view has been … rewrite facility. Even though query rewrite is enabled by default,

Database Data Warehousing Guide

Basic Query Rewrite

18 Basic Query RewriteThis chapter discusses query rewrite in Oracle, and contains: Overview of Query Rewrite Ensuring … that Query Rewrite Takes Effect Example of Query Rewrite

Database Data Warehousing Guide

Advanced Query Rewrite

Types of Query Rewriteoriginal tables. Query rewrite transforms an incoming query to fetch the results from materialized … answered almost instantaneously. For considerations regarding query rewrite of cube organized … used to rewrite a query: Text Match Rewrite Join Back

Database Data Warehousing Guide

Advanced Query Rewrite

Benefits of Using Dimensions A dimension defines a hierarchical parent/child relationships between columns,…If the dimensions are normalized, that is, stored in multiple tables, then check that a join between the dimension tables guarantees that each child-side row joins with one and only one parent-side row. In the case of denormalized dimensions, check that the child-side columns uniquely determine the parent-side (or attribute) columns. Failure to abide by these rules may result in incorrect results

Database Data Warehousing Guide

Advanced Query Rewrite

Query Rewrite in the Presence of Grouping Setsrow in the materialized view originates. Query rewrite can use the marker to distinguish what rows … materialized view: CREATE MATERIALIZED VIEW cust_postal_mv ENABLE QUERY REWRITE AS SELECT 1 AS marker … represent female customers in the first subselect of the UNION ALL. Note that query rewrite

Database Data Warehousing Guide

Advanced Query Rewrite

Using the EXPLAIN_REWRITE Procedure with Query RewriteIt can be difficult to understand why a query did not rewrite. The rules governing query rewrite … addition, you may want to know why query rewrite chose a particular materialized view instead of another … , you can take the appropriate action needed to make a query