264ddc9a67
Commit 44fb59fc6 taught the grouping-conflict walker to treat the arg
of a simple CASE as a direct operand of each WHEN comparison, but it
only checked the collation, on the assumption that the WHEN operator
is always the type-default "=" and thus matches the grouping eqop.
That assumption fails once the arg is relabeled to another type: the
WHEN then compares under that type's "=", which need not agree with
the grouping equality. For instance, with a DISTINCT over a citext
column, a qual such as "CASE t::text WHEN 'A' THEN ..." was pushed
below the Unique, although the equivalent "t::text = 'A'" is correctly
kept above it.
Instead of special-casing the arg, have the walker bind a Var arg
while walking the WHEN conditions and resolve each CaseTestExpr to it,
so that the arg is checked exactly as each WHEN uses it: with the
opfamily and collation checks of a direct operand when the WHEN is a
comparison, and as a non-operand reference otherwise. A non-Var arg
is walked once as a non-operand, as before. The CaseTestExpr in an
ArrayCoerceExpr's elemexpr and a JsonConstructorExpr's coercion stand
for something else and are left alone.
Reported-by: Tender Wang <tndrwang@gmail.com>
Author: Richard Guo <guofenglinux@gmail.com>
Reviewed-by: Tender Wang <tndrwang@gmail.com>
Reviewed-by: Ewan Young <kdbase.hack@gmail.com>
Discussion: https://postgr.es/m/CAHewXNkvGTOgijRLjmudpg=wz0d-J8ChY2o7ksh3Be+Q_Bxwog@mail.gmail.com
Backpatch-through: 18
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/.