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ExecEvalHashedScalarArrayOp(), when using a strict equality function, performs a short-circuit when looking up NULL values. When the function is non-strict, the code incorrectly looked up the hash table for a zero-valued Datum, which could have resulted in an accidental true return if the hash table contained zero valued Datum, or could result in a crash for non-byval types. Here we fix this by adding an extra step when we build the hash table to check what the result of a NULL lookup would be. This requires looping over the array and checking what the non-hashed version of the code would do. We cache the results of that in the expression so that we can reuse the result any time we're asked to search for a NULL value. It's important to note that non-strict equality functions are free to treat any NULL value as equal to any non-NULL value. For example, someone may wish to design a type that treats an empty string and NULL as equal. All built-in types have strict equality functions, so this could affect custom / user-defined types. Author: Chengpeng Yan <chengpeng_yan@outlook.com> Author: David Rowley <dgrowleyml@gmail.com> Reviewed-by: ChangAo Chen <cca5507@qq.com> Discussion: https://postgr.es/m/A16187AE-2359-4265-9F5E-71D015EC2B2D@outlook.com Backpatch-through: 14
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/.