Inner join example postgresql11/19/2023 ![]() However, that is not as simple as it may seem. We would like to write the query in a way that makes the PostgreSQL optimizer choose the plan we want. But we would like to join b and c first! Forcing the join order with an optimizer barrier The PostgreSQL optimizer decided to first join b and a, then join the result with c. The optimizer chooses the following plan: We have three tables a, b and c and want to calculate the natural join between them. In that case, read on for alternative ways to force the join order. This extension offers a comprehensive set of Oracle-style query hints, and it does not require a modified version of the PostgreSQL server.īut perhaps you don’t want to install third-party software, or your database is running at a hosting provider and you have no access to the operating system. ![]() If you really want query hints, you can get them: all you have to do is install the extension pg_hint_plan. However, one of the strong points of PostgreSQL is its extensibility. The discussion page references mailing list discussions that show that this decision has not been unanimous. ![]() The PostgreSQL TODO list lists optimizer hints under “Features We Do Not Want” and links to a discussion page that explains why. This article explains how you can influence execution plans in PostgreSQL. That makes it difficult to force the hand of the query planner when it comes to a certain join order that you know to be good. Administration join optimizer query tuning sql helpĭifferent from many other database systems, PostgreSQL does not support query hints.
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