What is query rewrite in Oracle?
The query rewrite mechanism in the Oracle server automatically rewrites the SQL query to use the summary tables. This mechanism reduces the response time for returning results from the query. Materialized views within the data warehouse are transparent to the end user or to the database application.
What is Authid Oracle?
Answer: The authid current_user is used when you want a piece of code (PL/SQL) to execute with the privileges of the current user, and NOT the user ID that created the procedure. PL/SQL, by default, run with the privileges of the schema within which they are created no matter who invokes the procedure.
Which is an example of a query rewriting?
Query Rewriting is a typically automatic transformation that takes a set of database tables views and/or queries, usually indices, often gathered data and query statistics, and other metadata, and yields a set of different queries, which produce the same results but execute with better performance (for example, faster, or with lower memory use).
How is a rewrite hint used in SQL?
Rewrite Hints. Hints can be included in 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 it regardless of the cost.
What are the benefits of query rewrite in SQL?
Overview of Query Rewrite. One of the major benefits of creating and maintaining materialized views is the ability to take advantage of query rewrite, which transforms a SQL statement expressed in terms of tables or views into a statement accessing one or more materialized views that are defined on the detail tables.
How does an optimizer rewrite a query block?
The optimizer rewrites a query by rewriting one or more query blocks, one at a time. If the rewrite logic has a choice between multiple materialized views to rewrite a query block, it will select the one which can result in reading in the least amount of data. After a materialized view has been picked for a rewrite, the optimizer performs the