What is meant by query optimization?

What is meant by query optimization?
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The phase that identifies an efficient execution plan for evaluating a query that has the least  estimated cost is referred to as query optimization.
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Related questions

Which of the following is not the function of client? A) Compile queries B) Query optimization C) Receive queries D) Result formatting and presentation

Description : Which of the following is not the function of client? A) Compile queries B) Query optimization C) Receive queries D) Result formatting and presentation

Last Answer : B) Query optimization

Which of the following is/are the Database server functions? i) Data management ii) Transaction management iii) Compile queries iv) Query optimization A) i, ii, and iv only B) i, ii and iii only C) ii, iii and iv only D) All i, ii, iii, and iv

Description : Which of the following is/are the Database server functions? i) Data management ii) Transaction management iii) Compile queries iv) Query optimization A) i, ii, and iv only B) i, ii and iii only C) ii, iii and iv only D) All i, ii, iii, and iv

Last Answer : A) i, ii, and iv only

What is RULE-based approach to optimization ?

Description : What is RULE-based approach to optimization ?

Last Answer : Choosing an executing planbased on the access paths available and the ranks of these access paths.

When is cost based optimization triggered? (for DBA

Description : When is cost based optimization triggered? (for DBA

Last Answer : It's important to have statistics on all tables for the CBO (Cost Based Optimizer) to work correctly. If one table involved in a statement does not have ... ANALYZE; 2. Change some initialization parameters (for example: hash_join_enabled, sort_area_size, db_file_multiblock_read_count).

What is COST-based approach to optimization ?

Description : What is COST-based approach to optimization ?

Last Answer : Considering available access paths and determining the most efficient execution plan based on statistics in the data dictionary for the tables accessed by the statement and their associated clusters and indexes.

What is the effect of setting the value "ALL_ROWS" for OPTIMIZER_GOAL parameter of the ALTER SESSION command ? What are the factors that affect OPTIMIZER in choosing an Optimization approach ?

Description : What is the effect of setting the value "ALL_ROWS" for OPTIMIZER_GOAL parameter of the ALTER SESSION command ? What are the factors that affect OPTIMIZER in choosing an Optimization approach ?

Last Answer : Answer The OPTIMIZER_MODE initialization parameter Statistics in the Data Dictionary the OPTIMIZER_GOAL parameter of the ALTER SESSION command hints in the statement.

What is Cost Based Optimization?

Description : What is Cost Based Optimization?

Last Answer : The Oracle Cost Based Optimizer (CBO) is a SQL Query optimizer that uses data statistics to identify the query plan with lowest cost before execution. The cost is based on the number of rows in ... Based Optimizer as the Rule Based Optimizer is not be supported in Oracle 10g and above releases.

If the maximum record retrieved property of the query is set to 10 then a summary value will be calculated?

Description : If the maximum record retrieved property of the query is set to 10 then a summary value will be calculated?

Last Answer : Only for 10 records.

What is a Query Record Group?

Description : What is a Query Record Group?

Last Answer : A query record group is a record group that has an associated SELECT statement. The columns in a query record group derive their default names, data types, had lengths from the database columns ... rows retrieved by the query associated with that record group. What is a Non Query Record Group?

What is the Difference between a post query and a pre query

Description : What is the Difference between a post query and a pre query

Last Answer : A post query will fire for every row that is fetched but the pre query will fire only once.

How you will avoid your query from using indexes?

Description : How you will avoid your query from using indexes?

Last Answer : SELECT * FROM emp Where emp_no+' '=12345; i.e you have to concatenate the column name with space within codes in the where condition. SELECT /*+ FULL(a) */ ename, emp_no from emp where emp_no=1234; i.e using HINTS

Suppose a customer table is having different columns like customer no, payments.What will be the query to select top three max payments?

Description : Suppose a customer table is having different columns like customer no, payments.What will be the query to select top three max payments?

Last Answer : SELECT customer_no, payments from customer C1 WHERE 3

What is correlated sub-query ?

Description : What is correlated sub-query ?

Last Answer : Correlated sub query is a sub query which has reference to the main query.

There is a % sign in one field of a column. What will be the query to find it?

Description : There is a % sign in one field of a column. What will be the query to find it?

Last Answer : '' Should be used before '%'.

How you will avoid duplicating records in a query?

Description : How you will avoid duplicating records in a query?

Last Answer : By using DISTINCT

My query was fine last week and now it is slow. Why? (for DBA

Description : My query was fine last week and now it is slow. Why? (for DBA

Last Answer : The likely cause of this is because the execution plan has changed. Generate a current explain plan of the offending query and compare it to a previous one that was taken when the query was ... the plan should be? Run the query with hints to see if this produces the required performance.

A query fetched 10 records How many times does a PRE- QUERY Trigger and POST-QUERY Trigger will get executed ?

Description : A query fetched 10 records How many times does a PRE-QUERY Trigger and POST-QUERY Trigger will get executed ?

Last Answer : PRE-QUERY fires once. POST-QUERY fires 10 times.

When is PRE-QUERY trigger executed ?

Description : When is PRE-QUERY trigger executed ?

Last Answer : When Execute-query or count-query Package procedures are invoked.

Why query fails sometimes ?

Description : Why query fails sometimes ?

Last Answer : Rollback segment dynamically extent to handle larger transactions entry loads. A single transaction may wipeout all available free space in the Rollback Segment Tablespace. This prevents other user using Rollback segments.

Where is the external query executed at the client or the server?

Description : Where is the external query executed at the client or the server?

Last Answer : At the server.

How is it possible to select generate a select set for the query in the query property sheet?

Description : How is it possible to select generate a select set for the query in the query property sheet?

Last Answer : By using the tables/columns button and then specifying the table and the column names.

What is a difference between pre-select and pre-query?

Description : What is a difference between pre-select and pre-query?

Last Answer : Fires during the execute query and count query processing after oracle forms constructs the select statement to be issued, but before the statement is actually issued. The pre-query trigger fires ... the query criteria in enter query mode.Pre-query trigger fires before pre-select trigger.

Is it possible to modify an external query in a report which contains it?

Description : Is it possible to modify an external query in a report which contains it?

Last Answer : No.

If a parameter is used in a query without being previously defined, what diff. exist betw. report 2.0 and 2.5 when the query is applied?

Description : If a parameter is used in a query without being previously defined, what diff. exist betw. report 2.0 and 2.5 when the query is applied?

Last Answer : While both reports 2.0 and 2.5 create the parameter, report 2.5 gives a message that a bind parameter has been created.

What is a query?

Description : What is a query?

Last Answer : A query with respect to DBMS relates to user commands that are used to interact with a data base. The query language can be classified into data definition language and data manipulation language.

What is Query evaluation engine?

Description : What is Query evaluation engine?

Last Answer : It executes low-level instruction generated by compiler.

What is meant by free extent ?

Description : What is meant by free extent ?

Last Answer : A free extent is a collection of continuous free blocks in tablespace. When a segment is dropped its extents are reallocated and are marked as free.

What is meant by redo log buffer ?

Description : What is meant by redo log buffer ?

Last Answer : Changes made to entries are written to the on-line redo log files. So that they can be used in roll forward operations during database recoveries. Before writing them into the redo log files ... buffers in SGA and LGWR will write into files frequently. LOG_BUFFER parameter will decide the size.

What is meant by recursive hints ?

Description : What is meant by recursive hints ?

Last Answer : Number of times processes repeatedly query the dictionary table is called recursive hints. It is due to the data dictionary cache is too small. By increasing the SHARED_POOL_SIZE parameter we can optimize the size of Data Dictionary Cache.

What is meant by Redo Log file mirroring ? How it can be achieved?

Description : What is meant by Redo Log file mirroring ? How it can be achieved?

Last Answer : Process of having a copy of redo log files is called mirroring. This can be achieved by creating group of log files together, so that LGWR will automatically writes them to all the members ... . If any one group fails then database automatically switch over to next group. It degrades performance.

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Okay...WHAT exactly is SEO (Search Engine Optimization)? Is it writing code? Is it programming? Web design? Can someone please clarify?

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what search engine optimization services?

Description : what search engine optimization services?

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Which and the best cleaning service and optimization of mac system?

Description : Which and the best cleaning service and optimization of mac system?

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Onpage Optimization for Ecommerce Website?

Description : Onpage Optimization for Ecommerce Website?

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Does search engine optimization can be considered as an ethical practice?

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How do you solve this optimization problem analytically?

Description : How do you solve this optimization problem analytically?

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Search Engine Optimization Marketing?

Description : Search Engine Optimization Marketing?

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