Oracle Transaction - Oracle (MCQ) questions and answers for Q. 5945

Q.  ___________________ determines the best possible way to execute a query.
- Published on 13 Aug 15

a. Transaction optimizer
b. Query optimizer
c. Optimizer
d. Oracle optimizer

ANSWER: Query optimizer

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  • Nirja Shah   -Posted on 22 Sep 15
    - The query optimizer (called simply the optimizer) is built-in database software that determines the most efficient method for a SQL statement to access requested data.

    - The optimizer attempts to generate the best execution plan for a SQL statement.

    - The best execution plan is defined as the plan with the lowest cost among all considered candidate plans.

    - The cost computation accounts for factors of query execution such as I/O, CPU, and communication.

    - The best method of execution depends on myriad conditions including how the query is written, the size of the data set, the layout of the data, and which access structures exist.

    - The optimizer determines the best plan for a SQL statement by examining multiple access methods, such as full table scan or index scans, and different join methods such as nested loops and hash joins.

    - Because the database has many internal statistics and tools at its disposal, the optimizer is usually in a better position than the user to determine the best method of statement execution.

    - For this reason, all SQL statements use the optimizer.

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