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nested loop joins - Mailing list pgsql-novice

From	Greg Rychlewski
Subject	nested loop joins
Date	October 26, 2021 21:47:50
Msg-id	CAKemG7Xi_3eS+wT97ENWbzAmpwoVHJ5=YbQQcnswo5G5qHaNMw@mail.gmail.com Whole thread Raw
Responses	Re: nested loop joins (Tom Lane <tgl@sss.pgh.pa.us>)
List	pgsql-novice

Hi,

I'm looking to understand how nested loop joins with limits work. Say I have this query

SELECT *

FROM a INNER JOIN b ON a.id = b.id

LIMIT 10;

Say this was done as a nested loop join where the rows of "a" are the outer loop.

In this scenario, would all the rows of "a" be materialized or are they lazily evaluated?

If they are lazily evaluated is it done using cursors?

Thanks

From: Alexey M Boltenkov
Date: 23 October 2021, 16:59:19
Subject: Re: Strange sequences - how to construct?

From: Tom Lane
Date: 26 October 2021, 21:56:12
Subject: Re: nested loop joins