postgres-github.git / summary / log / commit / refs

commit    ba82de48e62c633f5ad5e9dc9e6f2f3e8455a09f
Author:   Richard Guo <rguo@postgresql.org>
Date:     Fri May 08 01:57:50 2026 +0000

    Fix HAVING-to-WHERE pushdown for simple-CASE form
    
    Commit f76686ce7 added a walker that detects when a HAVING clause uses
    a collation that conflicts with the GROUP BY's nondeterministic
    collation, keeping such clauses in HAVING.  The walker uses
    exprInputCollation() to identify each ancestor's comparison collation,
    but missed the simple-CASE case: parse analysis builds each WHEN as
    OpExpr(CaseTestExpr op val), where CaseTestExpr is a placeholder for
    the arg, while the actual arg expression sits at cexpr->arg, outside
    the OpExpr that carries the comparison's inputcollid.  A GROUP Var at
    cexpr->arg was therefore visited with the WHEN's inputcollid absent
    from the ancestor stack, the conflict went undetected, and the clause
    was wrongly pushed to WHERE.
    
    Fix by handling simple CASE explicitly: before walking cexpr->arg,
    push every WHEN's inputcollid onto the ancestor stack so a GROUP Var
    at the arg is checked against the same collations the WHEN comparisons
    would apply.  Then walk the WHEN bodies and defresult under the
    unchanged stack, where their own collation contexts are picked up by
    the default path.
    
    Back-patch to v18 only; this fix extends the walker added by commit
    f76686ce7 and inherits its dependency on the v18 RTE_GROUP mechanism.
    
    Author: SATYANARAYANA NARLAPURAM <satyanarlapuram@gmail.com>
    Reviewed-by: Richard Guo <guofenglinux@gmail.com>
    Discussion: https://postgr.es/m/CAHg+QDcqPdd=2V0PQ_oNYj50OUeqSqznqFaYtP3RdokLBDXBqw@mail.gmail.com
    Backpatch-through: 18

[parent: 12ca57bf346f]