3f8c23c4d3
We have for a long time been able to prove implications and refutations between clauses structured like "expr op const" with the same subexpression and btree-related operators; for example that "x < 4" implies "x <= 5". The implication machinery is needed to detect usability of partial indexes, and the refutation machinery is needed to implement constraint exclusion. This patch extends that machinery to make proofs for operator expressions involving the same two immutable-but-not-necessarily-just-Const input expressions, ie does "expr1 op1 expr2" prove or refute "expr1 op2 expr2" or "expr2 op2 expr1"? An important example is that we can now prove "x = y" given "y = x", which formerly the code could not deduce unless x or y was a constant. We can make use of the system's knowledge of operator commutator and negator pairs, and can also make use of btree opclass relationships, for example "x < y" implies "x <= y" and refutes "x > y" (notice that neither of these could be proven just from commutator or negator links). Inspired by a gripe from Brian Dunavant. This seems more like a new feature than a bug fix, though, so no back-patch. |
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README
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: http://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 http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.