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 Plan:  Generating Query Plans, Database Tuning, Query Tuning

Famous quotes containing the words query and/or plan:

    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)

    As I write, there is a craze for what is called psychoanalysis, or the cure of diseases by explaining to the patient what is the matter with him: an excellent plan if you happen to know what is the matter with him, especially when the explanation is that there is nothing the matter with him.
    George Bernard Shaw (1856–1950)