It should only be used to provide more information to the optimizer that can improve the query performance. You might be able to improve the performance of a query by providing additional information to the optimizer, using what I like to call, a "Faux Predicate".ĭb=# ( SELECT * FROM sale WHERE modified < ' asia/tel_aviv' AND created < ' asia/tel_aviv' ) QUERY PLAN - Index Scan using sale_created_ix on sale (cost=0.44.4.52 rows=1 width=276) Index Cond: (created < ' 00:00:00+02'::timestamp with time zone) Filter: (modified < ' 00:00:00+02'::timestamp with time zone)Īfter we added the "Faux Predicate" the optimizer decided to use the index on the created field, and the query got much faster! Note that the previous predicate on the modified field is still being evaluated, but it's now being applied on much fewer rows.Ī "Faux Predicate" should not change the result of the query. In some circumstances, you have knowledge of your data that the optimizer does not have, or cannot have. In this case, it might conclude that it makes more sense to use an index rather than scan the entire table. For example, if you apply a filter on a column with a unique constraint, the optimizer knows it can expect exactly one row for each value. To generate a good execution plan, the optimizer utilizes metadata and statistics it has on your data. For example, the optimizer decides whether to use a specific index or not, in what order to execute a join, which table to filter first, and so on. The execution plan describes how the database in going to access the data necessary to satisfy the query. The query optimizer looks at your SQL and generates an execution plan. One of the most important components in database implementations, and usually the one that makes one database better than the other, is the query optimizer. Using BETWEEN incorrectly might produce overlapping results, for example, counting sales twice in two different periods. You can hide all irrelevant nodes (see node details), use horizontal or vertical plan layouts, export it to an image or save it as JSON to send to a colleague.SELECT * FROM sales WHERE created >= '' AND created < '' This visualization shows the most expensive (cost-based) plan nodes. In DBeaver Lite, Enterprise, and Ultimate editions you can use an advanced (graph) visualization of the execution plan. To see the source script on which the plan is based, click the View Source button ( ). To reevaluate the plan, click the Reevaluate button ( ). You can click the rows of the execution plan to see their details (statistics) in the panels below and to the right of the plan. The execution plan command generates a tree of query execution as one of the result tabs and is convenient in estimating if the query/script is quick/optimal enough: If a database driver supports the visualization of the execution plan, you can see the execution plan of the current query (under cursor) by pressing Ctrl+Shift+E or clicking Explain execution plan on the context menu or in the SQL Editor toolbar: (Note: toolbar is customizable. The Execution plan for databases marked with a star is supported only in Lite, Enterprise and Ultimate editions This feature is supported for the following data sources:
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