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For an inner_unique join, we always assume that the executor will stop scanning for matches after the first match. Therefore, for a mergejoin that is inner_unique and whose mergeclauses are sufficient to identify a match, we set the skip_mark_restore flag to true, indicating that the executor need not do mark/restore calls. However, merge-right-anti-join did not get this memo and continues scanning the inner side for matches after the first match. If there are duplicates in the outer scan, we may incorrectly skip matching some inner tuples, which can lead to wrong results. Here we fix this issue by ensuring that merge-right-anti-join also advances to next outer tuple after the first match in inner_unique cases. This also saves cycles by avoiding unnecessary scanning of inner tuples after the first match. Although hash-right-anti-join does not suffer from this wrong results issue, we apply the same change to it as well, to help save cycles for the same reason. Per bug #18522 from Antti Lampinen, and bug #18526 from Feliphe Pozzer. Back-patch to v16 where right-anti-join was introduced. Author: Richard Guo Discussion: https://postgr.es/m/18522-c7a8956126afdfd0@postgresql.org
PostgreSQL Database Management System
This directory contains the source code distribution of the PostgreSQL database management system.
PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings.
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