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Pushdown window functions (ROW_NUMBER, LEAD, MIN/MAX OVER) #175

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Merged
serprex merged 2 commits into from
Apr 4, 2026
Merged

Pushdown window functions (ROW_NUMBER, LEAD, MIN/MAX OVER) #175

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0caf913
Pushdown window functions (ROW_NUMBER, LEAD, MIN/MAX OVER)
iskakaushik Apr 2, 2026
8a374e8
Fix ORDER BY pushdown for window function queries
serprex Apr 4, 2026
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202 changes: 200 additions & 2 deletions src/deparse.c
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Original file line number Diff line number Diff line change
Expand Up @@ -160,6 +160,7 @@ static void deparseRangeTblRef(StringInfo buf, PlannerInfo * root,
RelOptInfo * foreignrel, bool make_subquery,
Index ignore_rel, List * *ignore_conds, List * *params_list);
static void deparseAggref(Aggref * node, deparse_expr_cxt * context);
static void deparseWindowFunc(WindowFunc * node, deparse_expr_cxt * context);
static void appendGroupByClause(List * tlist, deparse_expr_cxt * context);
static CustomObjectDef * appendFunctionName(Oid funcid, deparse_expr_cxt * context);
static Node * deparseSortGroupClause(Index ref, List * tlist, bool force_colno,
Expand Down Expand Up @@ -586,6 +587,28 @@ foreign_expr_walker(Node * node,
return false;
}
break;
case T_WindowFunc:
{
WindowFunc *wfunc = (WindowFunc *) node;

/* Not safe to pushdown when not in upper relation context */
if (!IS_UPPER_REL(glob_cxt->foreignrel))
return false;

/* The window function must be shippable */
if (!chfdw_is_shippable(wfunc->winfnoid, ProcedureRelationId, fpinfo, NULL))
return false;

/* FILTER is not supported in ClickHouse window functions */
if (wfunc->aggfilter)
return false;

/* Recurse to input arguments */
if (!foreign_expr_walker((Node *) wfunc->args,
glob_cxt))
return false;
}
break;
case T_CaseExpr:
{
CaseExpr *caseexpr = (CaseExpr *) node;
Expand Down Expand Up @@ -1805,6 +1828,9 @@ deparseExpr(Expr * node, deparse_expr_cxt * context)
case T_Aggref:
deparseAggref((Aggref *) node, context);
break;
case T_WindowFunc:
deparseWindowFunc((WindowFunc *) node, context);
break;
case T_CaseExpr:
deparseCaseExpr((CaseExpr *) node, context);
break;
Expand Down Expand Up @@ -3510,6 +3536,173 @@ deparseAggref(Aggref * node, deparse_expr_cxt * context)
context->func = cdef;
}

/*
* Deparse a WindowFunc node into context->buf.
*
* Generates: func_name(args) OVER (PARTITION BY ... ORDER BY ... frame)
*/
static void
deparseWindowFunc(WindowFunc * node, deparse_expr_cxt * context)
{
StringInfo buf = context->buf;
Query *query = context->root->parse;
WindowClause *wc;
ListCell *lc;
bool first;
char *funcname;

/* Find the WindowClause referenced by this WindowFunc */
wc = (WindowClause *) list_nth(query->windowClause, node->winref - 1);

/* Emit function name */
funcname = get_func_name(node->winfnoid);
CSTRING_TOLOWER(funcname);
appendStringInfoString(buf, funcname);
appendStringInfoChar(buf, '(');

/* Emit arguments */
first = true;
foreach(lc, node->args)
{
if (!first)
appendStringInfoString(buf, ", ");
first = false;
deparseExpr((Expr *) lfirst(lc), context);
}

appendStringInfoString(buf, ") OVER (");

/* PARTITION BY */
if (wc->partitionClause)
{
appendStringInfoString(buf, "PARTITION BY ");
first = true;
foreach(lc, wc->partitionClause)
{
SortGroupClause *sgc = (SortGroupClause *) lfirst(lc);
TargetEntry *tle = get_sortgroupref_tle(sgc->tleSortGroupRef,
query->targetList);

if (!first)
appendStringInfoString(buf, ", ");
first = false;
deparseExpr((Expr *) tle->expr, context);
}
}

/* ORDER BY */
if (wc->orderClause)
{
if (wc->partitionClause)
appendStringInfoChar(buf, ' ');
appendStringInfoString(buf, "ORDER BY ");
first = true;
foreach(lc, wc->orderClause)
{
SortGroupClause *sgc = (SortGroupClause *) lfirst(lc);
TargetEntry *tle = get_sortgroupref_tle(sgc->tleSortGroupRef,
query->targetList);
TypeCacheEntry *typentry;

if (!first)
appendStringInfoString(buf, ", ");
first = false;
deparseExpr((Expr *) tle->expr, context);

/* Determine sort direction from the sort operator */
typentry = lookup_type_cache(exprType((Node *) tle->expr),
TYPECACHE_LT_OPR | TYPECACHE_GT_OPR);
if (sgc->sortop == typentry->gt_opr)
appendStringInfoString(buf, " DESC");
else
appendStringInfoString(buf, " ASC");

if (sgc->nulls_first)
appendStringInfoString(buf, " NULLS FIRST");
}
}

/*
* Frame clause. We only emit non-default frames. The default is RANGE
* BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW when there is an ORDER BY,
* or RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING when there
* is no ORDER BY.
*/
if (wc->frameOptions != (FRAMEOPTION_DEFAULTS | FRAMEOPTION_NONDEFAULT) &&
(wc->frameOptions & FRAMEOPTION_NONDEFAULT))
{
appendStringInfoChar(buf, ' ');

/* Frame type */
if (wc->frameOptions & FRAMEOPTION_ROWS)
appendStringInfoString(buf, "ROWS ");
else if (wc->frameOptions & FRAMEOPTION_RANGE)
appendStringInfoString(buf, "RANGE ");
else if (wc->frameOptions & FRAMEOPTION_GROUPS)
appendStringInfoString(buf, "GROUPS ");

/* Frame start and end */
if (wc->frameOptions & FRAMEOPTION_BETWEEN)
{
appendStringInfoString(buf, "BETWEEN ");

/* Start bound */
if (wc->frameOptions & FRAMEOPTION_START_UNBOUNDED_PRECEDING)
appendStringInfoString(buf, "UNBOUNDED PRECEDING");
else if (wc->frameOptions & FRAMEOPTION_START_CURRENT_ROW)
appendStringInfoString(buf, "CURRENT ROW");
else if (wc->frameOptions & FRAMEOPTION_START_OFFSET_PRECEDING)
{
deparseExpr((Expr *) wc->startOffset, context);
appendStringInfoString(buf, " PRECEDING");
}
else if (wc->frameOptions & FRAMEOPTION_START_OFFSET_FOLLOWING)
{
deparseExpr((Expr *) wc->startOffset, context);
appendStringInfoString(buf, " FOLLOWING");
}

appendStringInfoString(buf, " AND ");

/* End bound */
if (wc->frameOptions & FRAMEOPTION_END_UNBOUNDED_FOLLOWING)
appendStringInfoString(buf, "UNBOUNDED FOLLOWING");
else if (wc->frameOptions & FRAMEOPTION_END_CURRENT_ROW)
appendStringInfoString(buf, "CURRENT ROW");
else if (wc->frameOptions & FRAMEOPTION_END_OFFSET_PRECEDING)
{
deparseExpr((Expr *) wc->endOffset, context);
appendStringInfoString(buf, " PRECEDING");
}
else if (wc->frameOptions & FRAMEOPTION_END_OFFSET_FOLLOWING)
{
deparseExpr((Expr *) wc->endOffset, context);
appendStringInfoString(buf, " FOLLOWING");
}
}
else
{
/* No BETWEEN — single start bound */
if (wc->frameOptions & FRAMEOPTION_START_UNBOUNDED_PRECEDING)
appendStringInfoString(buf, "UNBOUNDED PRECEDING");
else if (wc->frameOptions & FRAMEOPTION_START_CURRENT_ROW)
appendStringInfoString(buf, "CURRENT ROW");
else if (wc->frameOptions & FRAMEOPTION_START_OFFSET_PRECEDING)
{
deparseExpr((Expr *) wc->startOffset, context);
appendStringInfoString(buf, " PRECEDING");
}
else if (wc->frameOptions & FRAMEOPTION_START_OFFSET_FOLLOWING)
{
deparseExpr((Expr *) wc->startOffset, context);
appendStringInfoString(buf, " FOLLOWING");
}
}
}

appendStringInfoChar(buf, ')');
}

static void
deparseCaseExpr(CaseExpr * node, deparse_expr_cxt * context)
{
Expand Down Expand Up @@ -3753,11 +3946,16 @@ appendOrderByClause(List * pathkeys, bool has_final_sort,
{
/*
* By construction, context->foreignrel is the input relation to
* the final sort.
* the final sort. Upper rels may have an empty reltarget; fall
* back to the planner's upper target for that stage.
*/
PathTarget *target = context->foreignrel->reltarget;

if (target->exprs == NIL)
target = context->root->upper_targets[fpinfo->stage];
em_expr = chfdw_find_em_expr_for_input_target(context->root,
pathkey->pk_eclass,
context->foreignrel->reltarget);
target);
}
else if (IS_JOIN_REL(context->foreignrel) &&
fpinfo->jointype == JOIN_SEMI)
Expand Down
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