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Fix qual pushdown past grouping through simple CASE

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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
This commit is contained in:
Richard Guo
2026-09-02 15:32:54 +09:00
parent da7e446abb
commit dd7c135bb9
5 changed files with 176 additions and 46 deletions
Download Patch File Download Diff File Expand all files Collapse all files

137
src/backend/optimizer/util/clauses.c
View File

@@ -97,12 +97,15 @@ typedef struct
/*
* Walker context for expression_has_grouping_conflict. get_eqop is a callback
* that returns the equality operator used for grouping. cb_context is opaque
* to the walker and is forwarded to get_eqop unchanged.
* to the walker and is forwarded to get_eqop unchanged. case_var is the Var
* that the CaseTestExprs of the simple CASE being walked stand for, or NULL if
* there is none.
*/
typedef struct
{
grouping_eqop_callback get_eqop;
void *cb_context;
Var *case_var;
} grouping_walker_ctx;
static bool contain_agg_clause_walker(Node *node, void *context);
@@ -5515,6 +5518,7 @@ expression_has_grouping_conflict(Node *expr,
ctx.get_eqop = get_eqop;
ctx.cb_context = context;
ctx.case_var = NULL;
return grouping_conflict_walker(expr, &ctx);
}
@@ -5533,10 +5537,13 @@ expression_has_grouping_conflict(Node *expr,
* member, and RowCompareExpr (one operator and collation per column). A
* simple CASE (CaseExpr with a non-NULL arg) is a comparison in disguise:
* parse analysis builds each WHEN as "OpExpr(CaseTestExpr op val)", with the
* CaseTestExpr standing in for the arg, so the arg is effectively an operand
* of each WHEN's comparison. Those WHEN operators are always the type-default
* "=", matching the grouping eqop, so only a collation conflict is possible
* there.
* CaseTestExpr standing in for the arg. If the arg is a Var (after looking
* through RelabelType), it is bound in ctx->case_var while the WHEN
* conditions are walked and each CaseTestExpr is resolved to it, so the Var
* is checked exactly as each WHEN uses it. Any other arg is walked once as
* a non-operand and its CaseTestExprs are ignored, as are those in an
* ArrayCoerceExpr's elemexpr and a JsonConstructorExpr's coercion, which
* stand for something else.
*/
static bool
grouping_conflict_walker(Node *node, grouping_walker_ctx *ctx)
@@ -5603,54 +5610,88 @@ grouping_conflict_walker(Node *node, grouping_walker_ctx *ctx)
}
return false;
}
else if (IsA(node, CaseTestExpr))
{
/*
* A direct operand of a comparison is handled by
* grouping_check_operand; any other use is a non-operand reference to
* the Var it stands for, if any.
*/
return grouping_conflict_walker((Node *) ctx->case_var, ctx);
}
else if (IsA(node, ArrayCoerceExpr))
{
ArrayCoerceExpr *acexpr = (ArrayCoerceExpr *) node;
Var *save_case_var = ctx->case_var;
bool result;
if (grouping_conflict_walker((Node *) acexpr->arg, ctx))
return true;
/* The CaseTestExpr in elemexpr is an array element, not case_var. */
ctx->case_var = NULL;
result = grouping_conflict_walker((Node *) acexpr->elemexpr, ctx);
ctx->case_var = save_case_var;
return result;
}
else if (IsA(node, JsonConstructorExpr))
{
JsonConstructorExpr *ctor = (JsonConstructorExpr *) node;
Var *save_case_var = ctx->case_var;
bool result;
if (grouping_conflict_walker((Node *) ctor->args, ctx))
return true;
if (grouping_conflict_walker((Node *) ctor->func, ctx))
return true;
/* The CaseTestExpr in coercion is the JSON result, not case_var. */
ctx->case_var = NULL;
result = grouping_conflict_walker((Node *) ctor->coercion, ctx);
ctx->case_var = save_case_var;
return result;
}
else if (IsA(node, CaseExpr) && ((CaseExpr *) node)->arg != NULL)
{
CaseExpr *cexpr = (CaseExpr *) node;
Node *arg = (Node *) cexpr->arg;
Var *save_case_var = ctx->case_var;
bool result = false;
/* Look through RelabelType to find a direct Var arg. */
while (arg && IsA(arg, RelabelType))
arg = (Node *) ((RelabelType *) arg)->arg;
if (arg && IsA(arg, Var))
{
Var *var = (Var *) arg;
/*
* The arg is a grouping column compared by every WHEN. For a
* nondeterministic collation, reject if any WHEN applies a
* different collation.
*/
if (OidIsValid(ctx->get_eqop(var, ctx->cb_context)) &&
OidIsValid(var->varcollid) &&
!get_collation_isdeterministic(var->varcollid))
{
foreach_node(CaseWhen, cw, cexpr->args)
{
Oid collid = exprInputCollation((Node *) cw->expr);
if (OidIsValid(collid) && collid != var->varcollid)
return true;
}
}
}
else if (grouping_conflict_walker((Node *) cexpr->arg, ctx))
{
/* arg is a complex expression; walked as a non-operand */
return true;
}
/*
* Walk the WHEN conditions, their results, and the default result as
* non-operands. The WHEN conditions hold a CaseTestExpr in place of
* the arg, so they contribute no grouping operand of their own, but
* the condition expression or the substitution result may reference
* another grouping column.
* A Var arg needs no walk of its own: each WHEN condition refers to
* it through a CaseTestExpr, which is resolved to the Var and checked
* as the WHEN uses it. Any other arg is a non-operand reference in
* its own right: walk it once here and ignore its CaseTestExprs.
*/
if (arg && IsA(arg, Var))
ctx->case_var = (Var *) arg;
else
{
if (grouping_conflict_walker(arg, ctx))
return true;
ctx->case_var = NULL;
}
foreach_node(CaseWhen, cw, cexpr->args)
{
if (grouping_conflict_walker((Node *) cw->expr, ctx) ||
grouping_conflict_walker((Node *) cw->result, ctx))
if (grouping_conflict_walker((Node *) cw->expr, ctx))
{
result = true;
break;
}
}
ctx->case_var = save_case_var;
if (result)
return true;
/* The results and the default result contain no CaseTestExpr. */
foreach_node(CaseWhen, cw, cexpr->args)
{
if (grouping_conflict_walker((Node *) cw->result, ctx))
return true;
}
return grouping_conflict_walker((Node *) cexpr->defresult, ctx);
@@ -5683,12 +5724,13 @@ grouping_check_operands(Oid opno, Oid inputcollid, List *args,
* Handle one operand 'arg' of a comparison with operator 'opno' and
* collation 'inputcollid'.
*
* If 'arg' is a grouping column (after looking through RelabelType), verify
* that comparison's operator has equality semantics compatible with the
* grouping eqop and, for a nondeterministic collation, that it uses the same
* collation; such a direct operand is then fully handled and is not recursed
* into. Any other operand is walked normally, so a grouping column buried
* inside it is seen as a non-operand reference.
* If 'arg' is a grouping column (after looking through RelabelType, or through
* a CaseTestExpr to the Var it stands for), verify that comparison's operator
* has equality semantics compatible with the grouping eqop and, for a
* nondeterministic collation, that it uses the same collation; such a direct
* operand is then fully handled and is not recursed into. Any other operand
* is walked normally, so a grouping column buried inside it is seen as a
* non-operand reference.
*/
static bool
grouping_check_operand(Node *arg, Oid opno, Oid inputcollid,
@@ -5699,6 +5741,9 @@ grouping_check_operand(Node *arg, Oid opno, Oid inputcollid,
while (node && IsA(node, RelabelType))
node = (Node *) ((RelabelType *) node)->arg;
if (node && IsA(node, CaseTestExpr))
node = (Node *) ctx->case_var;
if (node && IsA(node, Var))
{
Var *var = (Var *) node;

35
src/test/regress/expected/collate.icu.utf8.out
View File

@@ -2344,6 +2344,41 @@ SELECT x, count(*) FROM test3ci GROUP BY x HAVING (CASE x WHEN 'abc' COLLATE cas
abc | 2
(1 row)
-- Positive: the WHEN value's own CaseTestExpr (JSON RETURNING coercion) does
-- not refer to the CASE arg
EXPLAIN (COSTS OFF)
SELECT x, count(*) FROM test3ci GROUP BY x HAVING (CASE x WHEN JSON_OBJECT('a': 'b' RETURNING text) THEN true ELSE false END);
QUERY PLAN
--------------------------------------------------------------------------------------------------
HashAggregate
Group Key: x
-> Seq Scan on test3ci
Filter: CASE x WHEN JSON_OBJECT('a' : 'b'::text RETURNING text) THEN true ELSE false END
(4 rows)
SELECT x, count(*) FROM test3ci GROUP BY x HAVING (CASE x WHEN JSON_OBJECT('a': 'b' RETURNING text) THEN true ELSE false END);
x | count
---+-------
(0 rows)
-- Positive: likewise for the CaseTestExpr in an ArrayCoerceExpr's elemexpr
CREATE DOMAIN nonempty_text AS text CHECK (VALUE <> '');
EXPLAIN (COSTS OFF)
SELECT x, count(*) FROM test3ci GROUP BY x HAVING (CASE x WHEN ('{abc}'::text[]::nonempty_text[])[1] THEN true ELSE false END);
QUERY PLAN
----------------------------------------------------------------------------------------------
HashAggregate
Group Key: x
-> Seq Scan on test3ci
Filter: CASE x WHEN (('{abc}'::text[])::nonempty_text[])[1] THEN true ELSE false END
(4 rows)
SELECT x, count(*) FROM test3ci GROUP BY x HAVING (CASE x WHEN ('{abc}'::text[]::nonempty_text[])[1] THEN true ELSE false END);
x | count
-----+-------
abc | 2
(1 row)
-- Negative: nested CASE with collation conflict
EXPLAIN (COSTS OFF)
SELECT x, count(*) FROM test3ci GROUP BY x HAVING (CASE WHEN (CASE x WHEN 'abc' COLLATE case_sensitive THEN 1 ELSE 0 END) = 1 THEN true ELSE false END);

27
src/test/regress/expected/subselect.out
View File

@@ -1930,6 +1930,33 @@ WHERE a = ROW(1.0)::t_rec;
1 | (1.00)
(1 row)
-- Simple CASE: the arg is compared by each WHEN, so the same rules apply.
-- The relabeled arg is compared by oid's "=", not the grouping eqop.
EXPLAIN (COSTS OFF)
SELECT * FROM (SELECT DISTINCT id FROM pdt) s
WHERE (CASE id::oid WHEN 1 THEN 1 ELSE 0 END) = 1;
QUERY PLAN
------------------------------------------------------------------
Subquery Scan on s
Filter: (CASE (s.id)::oid WHEN '1'::oid THEN 1 ELSE 0 END = 1)
-> HashAggregate
Group Key: pdt.id
-> Seq Scan on pdt
(5 rows)
-- Positive: compatible opfamily, safe to push past the grouping
EXPLAIN (COSTS OFF)
SELECT * FROM (SELECT DISTINCT id FROM pdt) s
WHERE (CASE id WHEN 1 THEN 1 ELSE 0 END) = 1;
QUERY PLAN
--------------------------------------------------------------
Unique
-> Sort
Sort Key: pdt.id
-> Seq Scan on pdt
Filter: (CASE id WHEN 1 THEN 1 ELSE 0 END = 1)
(5 rows)
-- Set operations: any operation other than UNION ALL groups rows by equality,
-- so the same opfamily-mismatch rules apply.
CREATE TEMP TABLE u1 (a t_rec);

12
src/test/regress/sql/collate.icu.utf8.sql
View File

@@ -827,6 +827,18 @@ EXPLAIN (COSTS OFF)
SELECT x, count(*) FROM test3ci GROUP BY x HAVING (CASE x WHEN 'abc' COLLATE case_insensitive THEN true ELSE false END);
SELECT x, count(*) FROM test3ci GROUP BY x HAVING (CASE x WHEN 'abc' COLLATE case_insensitive THEN true ELSE false END);
-- Positive: the WHEN value's own CaseTestExpr (JSON RETURNING coercion) does
-- not refer to the CASE arg
EXPLAIN (COSTS OFF)
SELECT x, count(*) FROM test3ci GROUP BY x HAVING (CASE x WHEN JSON_OBJECT('a': 'b' RETURNING text) THEN true ELSE false END);
SELECT x, count(*) FROM test3ci GROUP BY x HAVING (CASE x WHEN JSON_OBJECT('a': 'b' RETURNING text) THEN true ELSE false END);
-- Positive: likewise for the CaseTestExpr in an ArrayCoerceExpr's elemexpr
CREATE DOMAIN nonempty_text AS text CHECK (VALUE <> '');
EXPLAIN (COSTS OFF)
SELECT x, count(*) FROM test3ci GROUP BY x HAVING (CASE x WHEN ('{abc}'::text[]::nonempty_text[])[1] THEN true ELSE false END);
SELECT x, count(*) FROM test3ci GROUP BY x HAVING (CASE x WHEN ('{abc}'::text[]::nonempty_text[])[1] THEN true ELSE false END);
-- Negative: nested CASE with collation conflict
EXPLAIN (COSTS OFF)
SELECT x, count(*) FROM test3ci GROUP BY x HAVING (CASE WHEN (CASE x WHEN 'abc' COLLATE case_sensitive THEN 1 ELSE 0 END) = 1 THEN true ELSE false END);

11
src/test/regress/sql/subselect.sql
View File

@@ -972,6 +972,17 @@ WHERE a = ROW(1.0)::t_rec;
SELECT * FROM (SELECT DISTINCT ON (a) id, a FROM pdt ORDER BY a, id) s
WHERE a = ROW(1.0)::t_rec;
-- Simple CASE: the arg is compared by each WHEN, so the same rules apply.
-- The relabeled arg is compared by oid's "=", not the grouping eqop.
EXPLAIN (COSTS OFF)
SELECT * FROM (SELECT DISTINCT id FROM pdt) s
WHERE (CASE id::oid WHEN 1 THEN 1 ELSE 0 END) = 1;
-- Positive: compatible opfamily, safe to push past the grouping
EXPLAIN (COSTS OFF)
SELECT * FROM (SELECT DISTINCT id FROM pdt) s
WHERE (CASE id WHEN 1 THEN 1 ELSE 0 END) = 1;
-- Set operations: any operation other than UNION ALL groups rows by equality,
-- so the same opfamily-mismatch rules apply.
CREATE TEMP TABLE u1 (a t_rec);