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Former Member
Sep 01, 2015 at 02:49 PM

do not understand NARY NESTED LOOP JOIN explanation in queryprocessing documentation


Hi all,

I'm actually reading the book 'Performance and Tuning Series : Query processing and Abstract plans' from ASE 15.7

My english might not be that good but I don't understand the explanation about the NARY NESTED LOOP JOIN

"With a series of NESTED LOOP JOIN, a scan may eliminate rows based on searchable argument values initialized by an earlier scan. That scan may not be the one that immediately preceded the failing scan. With a series of NESTED LOOP JOINs, the previous scan would be completely drained although it has no effect on the failing scan. This could result in a significant amount of needless I/O. With NARY NESTED LOOP JOINs, the next row fetched comes from the scan that produced the failing searchable argument value, which is far more efficient."

Could anyone help me understanding the NARY NESTED LOOP JOIN?