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Databases & SQL vocabulary · Indexes and Query Performance

Query optimizer

Meaning in databases & SQL, with examples

nounCommon term

In databases & SQL, query optimizer means: The part of a database engine that looks at a query and the table statistics and picks the cheapest way to run it, producing the execution plan.

In Turkish: sorgu iyileştirici, sorgu optimize edici, optimizer

How it is used

Usually just 'the optimizer'. Most modern databases use a cost-based optimizer that relies on statistics, so outdated statistics lead to bad plans. When the optimizer chooses badly, people update statistics, rewrite the query or, as a last resort, add hints.

Example sentences

  1. The query optimizer ignored our new index because the statistics were out of date.

  2. After the upgrade, the query optimizer started choosing a different join order.

Common collocations

  • cost-based optimizer
  • optimizer statistics
  • optimizer hint
  • update statistics
  • execution planThe step-by-step strategy the database chooses to run a query, showing which indexes it uses, how tables are joined and how many rows it expects.
  • indexAn extra data structure built on one or more columns that lets the database find rows quickly without reading the whole table, like the index at the back of a book.
  • query tuningThe work of making slow queries faster by studying their execution plans and then adding indexes, rewriting SQL or changing database settings.
  • cardinalityEither the type of relationship between tables (one-to-one, one-to-many, many-to-many) or the number of distinct values in a column.

This word in other fields

The same English word can have a different meaning in another field:

More terms: Indexes and Query Performance

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