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For a LEFT JOIN, if any var from the right-hand side (RHS) is forced to null by upper-level quals but is known to be non-null for any matching row, the only way the upper quals can be satisfied is if the join fails to match, producing a null-extended row. Thus, we can treat this left join as an anti-join. Previously, this transformation was limited to cases where the join's own quals were strict for the var forced to null by upper qual levels. This patch extends the logic to check table constraints, leveraging the NOT NULL attribute information already available thanks to the infrastructure introduced by e2debb643. If a forced-null var belongs to the RHS and is defined as NOT NULL in the schema (and is not nullable due to lower-level outer joins), we know that the left join can be reduced to an anti-join. Note that to ensure the var is not nullable by any lower-level outer joins within the current subtree, we collect the relids of base rels that are nullable within each subtree during the first pass of the reduce-outer-joins process. This allows us to verify in the second pass that a NOT NULL var is indeed safe to treat as non-nullable. Based on a proposal by Nicolas Adenis-Lamarre, but this is not the original patch. Suggested-by: Nicolas Adenis-Lamarre <nicolas.adenis.lamarre@gmail.com> Author: Tender Wang <tndrwang@gmail.com> Co-authored-by: Richard Guo <guofenglinux@gmail.com> Discussion: https://postgr.es/m/CACPGbctKMDP50PpRH09in+oWbHtZdahWSroRstLPOoSDKwoFsw@mail.gmail.com
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.
Copyright and license information can be found in the file COPYRIGHT.
General documentation about this version of PostgreSQL can be found at https://www.postgresql.org/docs/devel/. In particular, information about building PostgreSQL from the source code can be found at https://www.postgresql.org/docs/devel/installation.html.
The latest version of this software, and related software, may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.