Query Plan

A query plan (or query execution plan) is an ordered set of steps used to access or modify information in a SQL relational database management system. This is a specific case of the relational model concept of access plans.

Since SQL is declarative, there are typically a large number of alternative ways to execute a given query, with widely varying performance. When a query is submitted to the database, the query optimizer evaluates some of the different, correct possible plans for executing the query and returns what it considers the best alternative. Because query optimizers are imperfect, database users and administrators sometimes need to manually examine and tune the plans produced by the optimizer to get better performance.

Read more about Query PlanGenerating Query Plans, Database Tuning, Query Tuning

Other articles related to "query plan, query":

Explain Plan - Generating Query Plans
... Some packages feature tools which will generate a graphical representation of a query plan ... to cause the DBMS to return a textual description of the query plan ... Another mechanism for retrieving the query plan involves querying a virtual database table after executing the query to be examined ...
Query Plan - Query Tuning
... The query optimizer will not always choose the best query plan for a given query ... In some databases the query plan can be reviewed, problems found, and then the query optimizer given hints on how to improve it ... alternatives to express the same query (other queries that return the same results) can be tried ...
Explain Plan - Query Tuning
... The query optimizer will not always choose the best query plan for a given query ... In some databases the query plan can be reviewed, problems found, and then the query optimizer given hints on how to improve it ... In other databases alternatives to express the same query (other queries that return the same results) can be tried ...

Famous quotes containing the words plan and/or query:

    Too many existing classrooms for young children have this overriding goal: To get the children ready for first grade. This goal is unworthy. It is hurtful. This goal has had the most distorting impact on five-year-olds. It causes kindergartens to be merely the handmaidens of first grade.... Kindergarten teachers cannot look at their own children and plan for their present needs as five-year-olds.
    James L. Hymes, Jr. (20th century)

    Such condition of suspended judgment indeed, in its more genial development and under felicitous culture, is but the expectation, the receptivity, of the faithful scholar, determined not to foreclose what is still a question—the “philosophic temper,” in short, for which a survival of query will be still the salt of truth, even in the most absolutely ascertained knowledge.
    Walter Pater (1839–1894)