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Since v15 we've had an option to apply a foreign key constraint's ON DELETE SET DEFAULT or SET NULL action to just some of the referencing columns. There was not a check for duplicate entries in the list of columns-to-set, though. That caused a potential memory stomp in CreateConstraintEntry(), which incautiously assumed that the list of columns-to-set couldn't be longer than the number of key columns. Even after fixing that, the case doesn't work because you get an error like "multiple assignments to same column" from the SQL command that is generated to do the update. We could either raise an error for duplicate columns or silently suppress the dups, and after a bit of thought I chose to do the latter. This is motivated by the fact that duplicates in the FK column list are legal, so it's not real clear why duplicates in the columns-to-set list shouldn't be. Of course there's no need to actually set the column more than once. I left in the fix in CreateConstraintEntry() too, just because it didn't seem like such low-level code ought to be making assumptions about what it's handed. Bug: #18879 Reported-by: Yu Liang <luy70@psu.edu> Author: Tom Lane <tgl@sss.pgh.pa.us> Discussion: https://postgr.es/m/18879-259fc59d072bd4d7@postgresql.org Backpatch-through: 15
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. PostgreSQL has many language interfaces, many of which are listed here: https://www.postgresql.org/download/ See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.