diff --git a/debug_query.sql b/debug_query.sql
new file mode 100644
index 000000000..4ffde825c
--- /dev/null
+++ b/debug_query.sql
@@ -0,0 +1,32 @@
+-- Debug query for PostgreSQL 18 compatibility issue
+\c citus
+
+SET citus.log_remote_commands = on;
+SET client_min_messages = DEBUG1;
+
+SELECT
+	DISTINCT user_id
+FROM
+	(
+		SELECT users_table.user_id FROM users_table,
+		(
+			SELECT
+				avg(event_type) as avg_val
+			FROM
+				(SELECT
+					event_type, users_table.user_id
+				 FROM
+				 	users_table, (SELECT user_id, event_type FROM events_table WHERE value_2 < 3 ORDER BY 1, 2 OFFSET 0) as foo
+				 WHERE
+				 	foo.user_id = users_table.user_id) bar, users_table
+			WHERE
+				bar.user_id = users_table.user_id
+		GROUP BY
+			users_table.value_1
+		) as baz
+		WHERE
+			baz.avg_val < users_table.user_id
+		ORDER BY 1
+		LIMIT 3
+	) as sub1
+	ORDER BY 1 DESC;
diff --git a/debug_test.sql b/debug_test.sql
new file mode 100644
index 000000000..b641615a8
--- /dev/null
+++ b/debug_test.sql
@@ -0,0 +1,15 @@
+
+-- Create a simple test to reproduce the issue
+CREATE SCHEMA debug_test;
+SET search_path TO debug_test, public;
+SET client_min_messages TO DEBUG1;
+
+-- Simple query that should generate intermediate results
+SELECT DISTINCT user_id FROM (
+    SELECT users_table.user_id 
+    FROM users_table 
+    WHERE user_id < 3
+    ORDER BY 1 
+    LIMIT 2
+) as sub1 ORDER BY 1 DESC;
+
diff --git a/regression.diffs b/regression.diffs
new file mode 100644
index 000000000..e69de29bb
diff --git a/regression.out b/regression.out
new file mode 100644
index 000000000..2ca51aa58
--- /dev/null
+++ b/regression.out
@@ -0,0 +1,2 @@
+# using postmaster on localhost, port 57636
+# diff command failed with status 512: diff  "/workspaces/citus/expected/subqueries_deep.out" "/workspaces/citus/results/subqueries_deep.out" > "/workspaces/citus/results/subqueries_deep.out.diff"Bail out!
diff --git a/results/subqueries_deep.out.diff b/results/subqueries_deep.out.diff
new file mode 100644
index 000000000..e69de29bb
diff --git a/setup_test_tables.sql b/setup_test_tables.sql
new file mode 100644
index 000000000..46f671150
--- /dev/null
+++ b/setup_test_tables.sql
@@ -0,0 +1,25 @@
+-- Setup test tables for PostgreSQL 18 compatibility testing
+\c citus
+
+SET citus.shard_replication_factor = 1;
+SET citus.shard_count = 4;
+
+-- Create tables if they don't exist
+CREATE TABLE IF NOT EXISTS users_table (user_id int, time timestamp, value_1 int, value_2 int, value_3 float, value_4 bigint);
+CREATE TABLE IF NOT EXISTS events_table (user_id int, time timestamp, event_type int, value_2 int, value_3 float, value_4 bigint);
+
+-- Create distributed tables
+SELECT create_distributed_table('users_table', 'user_id');
+SELECT create_distributed_table('events_table', 'user_id');
+
+-- Insert some test data
+INSERT INTO users_table VALUES 
+(1, now(), 10, 20, 1.5, 100),
+(2, now(), 30, 40, 2.5, 200),
+(3, now(), 50, 60, 3.5, 300);
+
+INSERT INTO events_table VALUES 
+(1, now(), 1, 1, 1.1, 10),
+(2, now(), 2, 2, 2.2, 20),
+(3, now(), 3, 3, 3.3, 30),
+(1, now(), 4, 4, 4.4, 40);
diff --git a/src/backend/distributed/deparser/citus_ruleutils.c b/src/backend/distributed/deparser/citus_ruleutils.c
index a25cdf5bb..9d54804d4 100644
--- a/src/backend/distributed/deparser/citus_ruleutils.c
+++ b/src/backend/distributed/deparser/citus_ruleutils.c
@@ -1869,15 +1869,22 @@ ExpandMergedSubscriptingRefEntries(List *targetEntryList)
 			Expr *refexpr = subsRef->refexpr;
 			subsRef->refexpr = NULL;
 
-			/*
-			 * Wrap the Expr that holds SubscriptingRef (directly or indirectly)
-			 * in a new TargetEntry; note that it doesn't have a refexpr anymore.
-			 */
-			TargetEntry *newTargetEntry = copyObject(targetEntry);
-			newTargetEntry->expr = expr;
-			expandedTargetEntries = lappend(expandedTargetEntries, newTargetEntry);
-
-			/* now inspect the refexpr that SubscriptingRef at hand were holding */
+		/*
+		 * Wrap the Expr that holds SubscriptingRef (directly or indirectly)
+		 * in a new TargetEntry; note that it doesn't have a refexpr anymore.
+		 */
+		TargetEntry *newTargetEntry = copyObject(targetEntry);
+		newTargetEntry->expr = expr;
+		
+		/*
+		 * PostgreSQL 18 compatibility: handle NULL or "?column?" resname
+		 */
+		if (newTargetEntry->resname == NULL || strcmp(newTargetEntry->resname, "?column?") == 0)
+		{
+			newTargetEntry->resname = psprintf("expr_col_%d", newTargetEntry->resno);
+		}
+		
+		expandedTargetEntries = lappend(expandedTargetEntries, newTargetEntry);			/* now inspect the refexpr that SubscriptingRef at hand were holding */
 			expr = refexpr;
 		}
 
diff --git a/src/backend/distributed/deparser/ruleutils_18.c b/src/backend/distributed/deparser/ruleutils_18.c
index 7d4b99741..d57c94466 100644
--- a/src/backend/distributed/deparser/ruleutils_18.c
+++ b/src/backend/distributed/deparser/ruleutils_18.c
@@ -2722,7 +2722,16 @@ get_simple_values_rte(Query *query, TupleDesc resultDesc)
 			if (resultDesc && colno <= resultDesc->natts)
 				colname = NameStr(TupleDescAttr(resultDesc, colno - 1)->attname);
 			else
+			{
 				colname = tle->resname;
+				/* PostgreSQL 18 compatibility: handle NULL resname */
+				if (colname == NULL || strcmp(colname, "?column?") == 0)
+				{
+					static char generated_name[64];
+					snprintf(generated_name, sizeof(generated_name), "intermediate_column_%d", colno);
+					colname = generated_name;
+				}
+			}
 
 			/* does it match the VALUES RTE? */
 			if (colname == NULL || strcmp(colname, cname) != 0)
@@ -2921,8 +2930,17 @@ get_target_list(List *targetList, deparse_context *context)
 			 * When colNamesVisible is true, we should always show the
 			 * assigned column name explicitly.  Otherwise, show it only if
 			 * it's not FigureColname's fallback.
+			 * 
+			 * PostgreSQL 18 fix: Instead of using "?column?" which causes issues
+			 * in complex subqueries, generate a meaningful column name.
 			 */
-			attname = context->colNamesVisible ? NULL : "?column?";
+			if (context->colNamesVisible)
+				attname = NULL;
+			else
+			{
+				/* Generate a column name that won't cause parsing issues */
+				attname = psprintf("expr_%d", colno);
+			}
 		}
 
 		/*
@@ -2935,7 +2953,23 @@ get_target_list(List *targetList, deparse_context *context)
 			colname = NameStr(TupleDescAttr(context->resultDesc,
 											colno - 1)->attname);
 		else
+		{
 			colname = tle->resname;
+			
+			/*
+			 * PostgreSQL 18 fix: tle->resname can be NULL for intermediate expressions.
+			 * In that case, generate a meaningful column name instead of using "?column?".
+			 */
+			if (colname == NULL || strcmp(colname, "?column?") == 0)
+			{
+				/*
+				 * Generate a column name in the format "col_N" where N is the column number.
+				 * This provides a stable, predictable name that won't cause issues with
+				 * column resolution in complex subqueries.
+				 */
+				colname = psprintf("col_%d", colno);
+			}
+		}
 
 		/* Show AS unless the column's name is correct as-is */
 		if (colname)			/* resname could be NULL */
@@ -4532,7 +4566,16 @@ get_variable(Var *var, int levelsup, bool istoplevel, deparse_context *context)
 				colname = NameStr(TupleDescAttr(context->resultDesc,
 												colno - 1)->attname);
 			else
+			{
 				colname = tle->resname;
+				/* PostgreSQL 18 compatibility: handle NULL resname */
+				if (colname == NULL || strcmp(colname, "?column?") == 0)
+				{
+					static char generated_name[64];
+					snprintf(generated_name, sizeof(generated_name), "intermediate_column_%d", colno);
+					colname = generated_name;
+				}
+			}
 			if (colname && strcmp(colname, attname) == 0 &&
 				!equal(var, tle->expr))
 			{
diff --git a/src/backend/distributed/planner/combine_query_planner.c b/src/backend/distributed/planner/combine_query_planner.c
index c8ab2a4b3..a8f39d419 100644
--- a/src/backend/distributed/planner/combine_query_planner.c
+++ b/src/backend/distributed/planner/combine_query_planner.c
@@ -110,6 +110,19 @@ RemoteScanTargetList(List *workerTargetList)
 		 * entry's sort and group clauses will *break* us here.
 		 */
 		TargetEntry *remoteScanTargetEntry = flatCopyTargetEntry(workerTargetEntry);
+		
+		/*
+		 * PostgreSQL 18 fix: Handle "?column?" names from intermediate expressions.
+		 * When flatCopyTargetEntry copies a target entry that has "?column?" as resname,
+		 * we need to generate a proper column name to avoid parsing errors.
+		 */
+		if (remoteScanTargetEntry->resname == NULL || strcmp(remoteScanTargetEntry->resname, "?column?") == 0)
+		{
+			StringInfo generatedName = makeStringInfo();
+			appendStringInfo(generatedName, "remote_col_%d", workerTargetEntry->resno);
+			remoteScanTargetEntry->resname = generatedName->data;
+		}
+		
 		remoteScanTargetEntry->expr = (Expr *) remoteScanColumn;
 		remoteScanTargetList = lappend(remoteScanTargetList, remoteScanTargetEntry);
 	}
@@ -272,7 +285,18 @@ BuildSelectStatementViaStdPlanner(Query *combineQuery, List *remoteScanTargetLis
 		TargetEntry *targetEntry = NULL;
 		foreach_declared_ptr(targetEntry, remoteScanTargetList)
 		{
-			columnNameList = lappend(columnNameList, makeString(targetEntry->resname));
+			char *resname = targetEntry->resname;
+			
+			/*
+			 * PostgreSQL 18 compatibility: handle NULL or "?column?" resname
+			 * by generating a proper column name for the remote scan RTE
+			 */
+			if (resname == NULL || strcmp(resname, "?column?") == 0)
+			{
+				resname = psprintf("remote_col_%d", targetEntry->resno);
+			}
+			
+			columnNameList = lappend(columnNameList, makeString(resname));
 		}
 		extradataContainerRTE->eref = makeAlias("remote_scan", columnNameList);
 	}
diff --git a/src/backend/distributed/planner/distributed_planner.c b/src/backend/distributed/planner/distributed_planner.c
index e22296ec7..34f114fff 100644
--- a/src/backend/distributed/planner/distributed_planner.c
+++ b/src/backend/distributed/planner/distributed_planner.c
@@ -1545,7 +1545,18 @@ FinalizeRouterPlan(PlannedStmt *localPlan, CustomScan *customScan)
 	TargetEntry *targetEntry = NULL;
 	foreach_declared_ptr(targetEntry, customScan->scan.plan.targetlist)
 	{
-		String *columnName = makeString(targetEntry->resname);
+		char *resname = targetEntry->resname;
+		
+		/*
+		 * PostgreSQL 18 compatibility: handle NULL or "?column?" resname
+		 * by generating a proper column name for the remote scan RTE
+		 */
+		if (resname == NULL || strcmp(resname, "?column?") == 0)
+		{
+			resname = psprintf("remote_col_%d", targetEntry->resno);
+		}
+		
+		String *columnName = makeString(resname);
 		columnNameList = lappend(columnNameList, columnName);
 	}
 
@@ -1613,6 +1624,19 @@ makeCustomScanTargetlistFromExistingTargetList(List *existingTargetlist)
 		}
 
 		TargetEntry *newTargetEntry = flatCopyTargetEntry(targetEntry);
+		
+		/*
+		 * PostgreSQL 18 fix: Handle "?column?" names from intermediate expressions.
+		 * When flatCopyTargetEntry copies a target entry that has "?column?" as resname,
+		 * we need to generate a proper column name to avoid parsing errors.
+		 */
+		if (newTargetEntry->resname == NULL || strcmp(newTargetEntry->resname, "?column?") == 0)
+		{
+			StringInfo generatedName = makeStringInfo();
+			appendStringInfo(generatedName, "custom_col_%d", targetEntry->resno);
+			newTargetEntry->resname = generatedName->data;
+		}
+		
 		newTargetEntry->expr = (Expr *) newVar;
 		custom_scan_tlist = lappend(custom_scan_tlist, newTargetEntry);
 	}
diff --git a/src/backend/distributed/planner/insert_select_planner.c b/src/backend/distributed/planner/insert_select_planner.c
index 3bf0bb327..6b03b3602 100644
--- a/src/backend/distributed/planner/insert_select_planner.c
+++ b/src/backend/distributed/planner/insert_select_planner.c
@@ -654,6 +654,18 @@ CreateTargetListForCombineQuery(List *targetList)
 	foreach_declared_ptr(originalTargetEntry, targetList)
 	{
 		TargetEntry *newTargetEntry = flatCopyTargetEntry(originalTargetEntry);
+		
+		/*
+		 * PostgreSQL 18 fix: Handle "?column?" names from intermediate expressions.
+		 * When flatCopyTargetEntry copies a target entry that has "?column?" as resname,
+		 * we need to generate a proper column name to avoid parsing errors.
+		 */
+		if (newTargetEntry->resname == NULL || strcmp(newTargetEntry->resname, "?column?") == 0)
+		{
+			StringInfo generatedName = makeStringInfo();
+			appendStringInfo(generatedName, "insert_col_%d", originalTargetEntry->resno);
+			newTargetEntry->resname = generatedName->data;
+		}
 
 		Var *column = makeVarFromTargetEntry(masterTableId, originalTargetEntry);
 		column->varattno = columnId;
@@ -1116,6 +1128,14 @@ ReorderInsertSelectTargetLists(Query *originalQuery, RangeTblEntry *insertRte,
 
 			newSubqueryTargetEntry = copyObject(oldSubqueryTle);
 
+			/*
+			 * PostgreSQL 18 compatibility: handle NULL or "?column?" resname
+			 */
+			if (newSubqueryTargetEntry->resname == NULL || strcmp(newSubqueryTargetEntry->resname, "?column?") == 0)
+			{
+				newSubqueryTargetEntry->resname = psprintf("expr_col_%d", newSubqueryTargetEntry->resno);
+			}
+
 			newSubqueryTargetEntry->resno = resno;
 			newSubqueryTargetlist = lappend(newSubqueryTargetlist,
 											newSubqueryTargetEntry);
@@ -1130,7 +1150,17 @@ ReorderInsertSelectTargetLists(Query *originalQuery, RangeTblEntry *insertRte,
 											newSubqueryTargetEntry);
 		}
 
-		String *columnName = makeString(newSubqueryTargetEntry->resname);
+		/*
+		 * PostgreSQL 18 compatibility: handle NULL or "?column?" resname
+		 * before creating columnName for eref->colnames
+		 */
+		char *resname = newSubqueryTargetEntry->resname;
+		if (resname == NULL || strcmp(resname, "?column?") == 0)
+		{
+			resname = psprintf("insert_col_%d", newSubqueryTargetEntry->resno);
+		}
+		
+		String *columnName = makeString(resname);
 		columnNameList = lappend(columnNameList, columnName);
 
 		/*
@@ -1175,6 +1205,14 @@ ReorderInsertSelectTargetLists(Query *originalQuery, RangeTblEntry *insertRte,
 
 		TargetEntry *newSubqueryTargetEntry = copyObject(oldSubqueryTle);
 
+		/*
+		 * PostgreSQL 18 compatibility: handle NULL or "?column?" resname
+		 */
+		if (newSubqueryTargetEntry->resname == NULL || strcmp(newSubqueryTargetEntry->resname, "?column?") == 0)
+		{
+			newSubqueryTargetEntry->resname = psprintf("expr_col_%d", newSubqueryTargetEntry->resno);
+		}
+
 		newSubqueryTargetEntry->resno = resno;
 		newSubqueryTargetlist = lappend(newSubqueryTargetlist,
 										newSubqueryTargetEntry);
diff --git a/src/backend/distributed/planner/multi_logical_optimizer.c b/src/backend/distributed/planner/multi_logical_optimizer.c
index 7deced084..e7205d029 100644
--- a/src/backend/distributed/planner/multi_logical_optimizer.c
+++ b/src/backend/distributed/planner/multi_logical_optimizer.c
@@ -1430,6 +1430,18 @@ MasterExtendedOpNode(MultiExtendedOp *originalOpNode,
 		TargetEntry *newTargetEntry = flatCopyTargetEntry(originalTargetEntry);
 		Expr *originalExpression = originalTargetEntry->expr;
 		Expr *newExpression = NULL;
+		
+		/*
+		 * PostgreSQL 18 fix: Handle "?column?" names from intermediate expressions.
+		 * When flatCopyTargetEntry copies a target entry that has "?column?" as resname,
+		 * we need to generate a proper column name to avoid parsing errors on workers.
+		 */
+		if (newTargetEntry->resname == NULL || strcmp(newTargetEntry->resname, "?column?") == 0)
+		{
+			StringInfo generatedName = makeStringInfo();
+			appendStringInfo(generatedName, "expr_col_%d", originalTargetEntry->resno);
+			newTargetEntry->resname = generatedName->data;
+		}
 
 		if (CanPushDownExpression((Node *) originalExpression, extendedOpNodeProperties))
 		{
@@ -2947,7 +2959,7 @@ GenerateWorkerTargetEntry(TargetEntry *targetEntry, Expr *workerExpression,
 		newTargetEntry = makeNode(TargetEntry);
 	}
 
-	if (newTargetEntry->resname == NULL)
+	if (newTargetEntry->resname == NULL || strcmp(newTargetEntry->resname, "?column?") == 0)
 	{
 		newTargetEntry->resname = WorkerColumnName(targetProjectionNumber);
 	}
diff --git a/src/backend/distributed/planner/multi_physical_planner.c b/src/backend/distributed/planner/multi_physical_planner.c
index e0f4c4332..3e6ba00ff 100644
--- a/src/backend/distributed/planner/multi_physical_planner.c
+++ b/src/backend/distributed/planner/multi_physical_planner.c
@@ -1436,6 +1436,29 @@ ExtractColumns(RangeTblEntry *callingRTE, int rangeTableId,
 			  columnNames,
 			  columnVars);
 #endif
+
+#if PG_VERSION_NUM >= PG_VERSION_18
+	/*
+	 * PostgreSQL 18 compatibility: expandRTE might return NULL or "?column?" names
+	 * for intermediate expressions. Fix these column names to avoid errors.
+	 */
+	List *fixedColumnNames = NIL;
+	ListCell *nameCell = NULL;
+	int colIndex = 1;
+	
+	foreach(nameCell, *columnNames)
+	{
+		char *colName = strVal(lfirst(nameCell));
+		if (colName == NULL || strcmp(colName, "?column?") == 0)
+		{
+			colName = psprintf("expand_col_%d", colIndex);
+		}
+		fixedColumnNames = lappend(fixedColumnNames, makeString(colName));
+		colIndex++;
+	}
+	
+	*columnNames = fixedColumnNames;
+#endif
 }
 
 
diff --git a/src/backend/distributed/planner/recursive_planning.c b/src/backend/distributed/planner/recursive_planning.c
index 9db6481cb..14871393f 100644
--- a/src/backend/distributed/planner/recursive_planning.c
+++ b/src/backend/distributed/planner/recursive_planning.c
@@ -305,6 +305,32 @@ RecursivelyPlanSubqueriesAndCTEs(Query *query, RecursivePlanningContext *context
 	/* descend into subqueries */
 	query_tree_walker(query, RecursivelyPlanSubqueryWalker, context, 0);
 
+	/*
+	 * PostgreSQL 18 may generate NULL or "?column?" as column names
+	 * for intermediate results. After subquery replacement, we need to fix
+	 * any remaining "?column?" references in the main query's target list.
+	 */
+	ListCell *targetEntryCell = NULL;
+	int columnNumber = 1;
+	foreach(targetEntryCell, query->targetList)
+	{
+		TargetEntry *targetEntry = (TargetEntry *) lfirst(targetEntryCell);
+		
+		if (targetEntry->resjunk)
+		{
+			continue;
+		}
+		
+		if (targetEntry->resname == NULL || strcmp(targetEntry->resname, "?column?") == 0)
+		{
+			StringInfo generatedName = makeStringInfo();
+			appendStringInfo(generatedName, "main_query_column_%d", columnNumber);
+			targetEntry->resname = generatedName->data;
+		}
+		
+		columnNumber++;
+	}
+
 	/*
 	 * At this point, all CTEs, leaf subqueries containing local tables and
 	 * non-pushdownable subqueries have been replaced. We now check for
@@ -1170,6 +1196,32 @@ RecursivelyPlanCTEs(Query *query, RecursivePlanningContext *planningContext)
 
 		uint32 subPlanId = list_length(planningContext->subPlanList) + 1;
 
+		/*
+		 * PostgreSQL 18 may generate NULL or "?column?" as column names
+		 * for intermediate results. We need to fix these before the subquery
+		 * gets planned, as the intermediate result files will use these names.
+		 */
+		ListCell *targetEntryCell = NULL;
+		int columnNumber = 1;
+		foreach(targetEntryCell, subquery->targetList)
+		{
+			TargetEntry *targetEntry = (TargetEntry *) lfirst(targetEntryCell);
+			
+			if (targetEntry->resjunk)
+			{
+				continue;
+			}
+			
+			if (targetEntry->resname == NULL || strcmp(targetEntry->resname, "?column?") == 0)
+			{
+				StringInfo generatedName = makeStringInfo();
+				appendStringInfo(generatedName, "intermediate_column_%d", columnNumber);
+				targetEntry->resname = generatedName->data;
+			}
+			
+			columnNumber++;
+		}
+
 		if (IsLoggableLevel(DEBUG1))
 		{
 			StringInfo subPlanString = makeStringInfo();
@@ -1272,6 +1324,32 @@ RecursivelyPlanSubqueryWalker(Node *node, RecursivePlanningContext *context)
 	{
 		Query *query = (Query *) node;
 
+		/*
+		 * PostgreSQL 18 may generate NULL or "?column?" as column names
+		 * for intermediate results. Fix these before processing any subqueries
+		 * that might reference this query's target list.
+		 */
+		ListCell *targetEntryCell = NULL;
+		int columnNumber = 1;
+		foreach(targetEntryCell, query->targetList)
+		{
+			TargetEntry *targetEntry = (TargetEntry *) lfirst(targetEntryCell);
+			
+			if (targetEntry->resjunk)
+			{
+				continue;
+			}
+			
+			if (targetEntry->resname == NULL || strcmp(targetEntry->resname, "?column?") == 0)
+			{
+				StringInfo generatedName = makeStringInfo();
+				appendStringInfo(generatedName, "walker_query_column_%d_%d", context->level, columnNumber);
+				targetEntry->resname = generatedName->data;
+			}
+			
+			columnNumber++;
+		}
+
 		context->level += 1;
 
 		/*
@@ -1569,6 +1647,31 @@ RecursivelyPlanSubquery(Query *subquery, RecursivePlanningContext *planningConte
 		debugQuery = copyObject(subquery);
 	}
 
+	/*
+	 * PostgreSQL 18 may generate NULL or "?column?" as column names
+	 * for intermediate results. We need to fix these before the subquery
+	 * gets planned, as the intermediate result files will use these names.
+	 */
+	ListCell *targetEntryCell = NULL;
+	int columnNumber = 1;
+	foreach(targetEntryCell, subquery->targetList)
+	{
+		TargetEntry *targetEntry = (TargetEntry *) lfirst(targetEntryCell);
+		
+		if (targetEntry->resjunk)
+		{
+			continue;
+		}
+		
+		if (targetEntry->resname == NULL || strcmp(targetEntry->resname, "?column?") == 0)
+		{
+			StringInfo generatedName = makeStringInfo();
+			appendStringInfo(generatedName, "intermediate_column_%d", columnNumber);
+			targetEntry->resname = generatedName->data;
+		}
+		
+		columnNumber++;
+	}
 
 	/*
 	 * Create the subplan and append it to the list in the planning context.
@@ -1937,9 +2040,16 @@ GenerateRequiredColNamesFromTargetList(List *targetList)
 			 * column names of the inner subquery should only contain the
 			 * required columns, as in if we choose 'b' from ('a','b') colnames
 			 * should be 'a' not ('a','b')
+			 * 
+			 * PostgreSQL 18 compatibility: handle NULL or "?column?" resname
 			 */
-			innerSubqueryColNames = lappend(innerSubqueryColNames, makeString(
-												entry->resname));
+			char *resname = entry->resname;
+			if (resname == NULL || strcmp(resname, "?column?") == 0)
+			{
+				resname = psprintf("subquery_col_%d", entry->resno);
+			}
+			
+			innerSubqueryColNames = lappend(innerSubqueryColNames, makeString(resname));
 		}
 	}
 	return innerSubqueryColNames;
@@ -2482,6 +2592,17 @@ BuildReadIntermediateResultsQuery(List *targetEntryList, List *columnAliasList,
 			continue;
 		}
 
+		/*
+		 * PostgreSQL 18 may generate NULL or "?column?" as column names
+		 * for intermediate results. Generate a proper column name in such cases.
+		 */
+		if (columnName == NULL || strcmp(columnName, "?column?") == 0)
+		{
+			StringInfo generatedName = makeStringInfo();
+			appendStringInfo(generatedName, "intermediate_column_%d", columnNumber);
+			columnName = generatedName->data;
+		}
+
 		funcColNames = lappend(funcColNames, makeString(columnName));
 		funcColTypes = lappend_int(funcColTypes, columnType);
 		funcColTypMods = lappend_int(funcColTypMods, columnTypMod);
diff --git a/src/test/regress/coordinator_logfile b/src/test/regress/coordinator_logfile
new file mode 100644
index 000000000..564e1ae05
--- /dev/null
+++ b/src/test/regress/coordinator_logfile
@@ -0,0 +1,16 @@
+2025-08-02 06:34:55.234 UTC [41803] LOG:  starting PostgreSQL 18beta2 on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0, 64-bit
+2025-08-02 06:34:55.235 UTC [41803] LOG:  could not bind IPv6 address "::1": Address already in use
+2025-08-02 06:34:55.235 UTC [41803] HINT:  Is another postmaster already running on port 9700? If not, wait a few seconds and retry.
+2025-08-02 06:34:55.235 UTC [41803] LOG:  could not bind IPv4 address "127.0.0.1": Address already in use
+2025-08-02 06:34:55.235 UTC [41803] HINT:  Is another postmaster already running on port 9700? If not, wait a few seconds and retry.
+2025-08-02 06:34:55.235 UTC [41803] WARNING:  could not create listen socket for "localhost"
+2025-08-02 06:34:55.235 UTC [41803] FATAL:  could not create any TCP/IP sockets
+2025-08-02 06:34:55.240 UTC [41803] LOG:  database system is shut down
+2025-08-02 06:35:12.489 UTC [42020] LOG:  starting PostgreSQL 18beta2 on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0, 64-bit
+2025-08-02 06:35:12.490 UTC [42020] LOG:  could not bind IPv6 address "::1": Address already in use
+2025-08-02 06:35:12.490 UTC [42020] HINT:  Is another postmaster already running on port 9700? If not, wait a few seconds and retry.
+2025-08-02 06:35:12.490 UTC [42020] LOG:  could not bind IPv4 address "127.0.0.1": Address already in use
+2025-08-02 06:35:12.490 UTC [42020] HINT:  Is another postmaster already running on port 9700? If not, wait a few seconds and retry.
+2025-08-02 06:35:12.490 UTC [42020] WARNING:  could not create listen socket for "localhost"
+2025-08-02 06:35:12.490 UTC [42020] FATAL:  could not create any TCP/IP sockets
+2025-08-02 06:35:12.494 UTC [42020] LOG:  database system is shut down
diff --git a/test_aggregate_pg18.sql b/test_aggregate_pg18.sql
new file mode 100644
index 000000000..a78433750
--- /dev/null
+++ b/test_aggregate_pg18.sql
@@ -0,0 +1,25 @@
+-- Test aggregate with GROUP BY to isolate the problem
+\c citus
+
+-- Tables should already exist
+CREATE TABLE IF NOT EXISTS users_table (user_id int, value_1 int, value_2 int);
+CREATE TABLE IF NOT EXISTS events_table (user_id int, event_type int, value_2 int);
+
+-- Populate with minimal data
+INSERT INTO users_table (user_id, value_1, value_2) VALUES (1, 10, 100), (2, 20, 200) ON CONFLICT DO NOTHING;
+INSERT INTO events_table (user_id, event_type, value_2) VALUES (1, 1, 1), (2, 2, 2) ON CONFLICT DO NOTHING;
+
+-- Test simple aggregate without GROUP BY (should work)
+SELECT avg(event_type) FROM events_table;
+
+-- Test simple aggregate with GROUP BY (might fail)
+SELECT avg(event_type) FROM events_table GROUP BY user_id;
+
+-- Test nested aggregate with GROUP BY (likely to fail)
+SELECT avg(event_type) 
+FROM (
+    SELECT event_type, user_id
+    FROM events_table 
+    WHERE value_2 < 3
+) sub
+GROUP BY sub.user_id;
diff --git a/test_debug_detailed.sql b/test_debug_detailed.sql
new file mode 100644
index 000000000..b8a72d8d0
--- /dev/null
+++ b/test_debug_detailed.sql
@@ -0,0 +1,32 @@
+-- Debug test with detailed logging
+\c citus
+
+SET client_min_messages TO DEBUG2;
+SET citus.log_remote_commands TO ON;
+
+-- Test the failing query with detailed logging
+SELECT DISTINCT user_id
+FROM (
+    SELECT users_table.user_id 
+    FROM users_table,
+    (
+        SELECT avg(event_type) as avg_val
+        FROM (
+            SELECT event_type, users_table.user_id
+            FROM users_table, 
+            (
+                SELECT user_id, event_type 
+                FROM events_table 
+                WHERE value_2 < 3 
+                ORDER BY 1, 2 
+                LIMIT 1
+            ) as foo
+            WHERE foo.user_id = users_table.user_id
+        ) bar, users_table
+        WHERE bar.user_id = users_table.user_id
+        GROUP BY users_table.value_1
+    ) as baz
+    WHERE baz.avg_val < users_table.user_id
+    ORDER BY 1
+    LIMIT 1
+) as sub1;
diff --git a/test_debug_pg18.sql b/test_debug_pg18.sql
new file mode 100644
index 000000000..25a3e1791
--- /dev/null
+++ b/test_debug_pg18.sql
@@ -0,0 +1,116 @@
+-- Test to debug PostgreSQL 1-- Test the actual failing pattern before
+        SELECT users_table.value_1 as value1
+        FROM (
+            SELECT event_type, users_table.user_id
+            FROM users_table, 
+            (
+                SELECT user_id, event_type 
+                FROM events_table 
+                WHERE value_2 < 3 
+                ORDER BY 1, 2 
+                LIMIT 1
+            ) as foo
+            WHERE foo.user_id = users_table.user_id
+        ) bar, users_table
+        WHERE bar.user_id = users_table.user_id
+        GROUP BY value1;
+-- First let's test with our existing setup
+\c citus
+
+-- Simple subquery that should work
+SELECT user_id FROM (SELECT user_id FROM users_table WHERE user_id = 1) sub;
+
+-- Test aggregate subquery (this might have ?column? issue)
+SELECT * FROM (SELECT avg(user_id) FROM users_table) sub;
+
+-- Test complex subquery similar to the failing one
+SELECT * FROM (
+    SELECT avg(event_type) as avg_val
+    FROM (
+        SELECT event_type 
+        FROM events_table 
+        WHERE value_2 < 3 
+        LIMIT 1
+    ) foo
+) bar;
+
+--Test simple alias
+SELECT value_1 as value1
+from ( 
+    select * from (
+        select * from users_table
+    ) as tab2 
+) as tab;
+
+-- Test the actual failing pattern before
+        SELECT users_table.value_1 as value1
+        FROM (
+            SELECT event_type, users_table.user_id
+            FROM users_table, 
+            (
+                SELECT user_id, event_type 
+                FROM events_table 
+                WHERE value_2 < 3 
+                ORDER BY 1, 2 
+                LIMIT 1
+            ) as foo
+            WHERE foo.user_id = users_table.user_id
+        ) bar, users_table
+        WHERE bar.user_id = users_table.user_id
+   ;
+
+-- Test the actual failing pattern
+-- Test the simplified ?column? issue
+SELECT DISTINCT user_id
+FROM (
+    SELECT users_table.user_id 
+    FROM users_table,
+    (
+        SELECT event_type as avg_val
+        FROM (
+            SELECT event_type, a_users.user_id
+            FROM users_table as a_users, 
+            (
+                SELECT user_id, event_type 
+                FROM events_table 
+                WHERE value_2 < 3 
+                ORDER BY 1, 2 
+                LIMIT 1
+            ) as foo
+            WHERE foo.user_id = a_users.user_id
+        ) bar, users_table as b_users
+        WHERE bar.user_id = b_users.user_id
+    ) as baz
+    WHERE baz.avg_val < users_table.user_id
+    ORDER BY 1
+    LIMIT 1
+) as sub1;
+
+
+-- Test the actual failing pattern
+-- Test the simplified ?column? issue
+SELECT DISTINCT user_id
+FROM (
+    SELECT users_table.user_id 
+    FROM users_table,
+    (
+        SELECT avg(event_type) as avg_val
+        FROM (
+            SELECT event_type, a_users.user_id
+            FROM users_table as a_users, 
+            (
+                SELECT user_id, event_type 
+                FROM events_table 
+                WHERE value_2 < 3 
+                ORDER BY 1, 2 
+                LIMIT 1
+            ) as foo
+            WHERE foo.user_id = a_users.user_id
+        ) bar, users_table as b_users
+        WHERE bar.user_id = b_users.user_id
+        GROUP BY b_users.value_1
+    ) as baz
+    WHERE baz.avg_val < users_table.user_id
+    ORDER BY 1
+    LIMIT 1
+) as sub1;
\ No newline at end of file
diff --git a/test_failing_query.sql b/test_failing_query.sql
new file mode 100644
index 000000000..b2acbd8e9
--- /dev/null
+++ b/test_failing_query.sql
@@ -0,0 +1,21 @@
+-- Test only the failing complex nested query
+\c citus
+
+SET client_min_messages TO DEBUG5;
+
+-- The exact failing pattern (this should fail without our fix)
+SELECT avg(event_type) as avg_val
+FROM (
+    SELECT event_type, a_users.user_id
+    FROM users_table as a_users, 
+    (
+        SELECT user_id, event_type 
+        FROM events_table 
+        WHERE value_2 < 3 
+        ORDER BY 1, 2 
+        LIMIT 1
+    ) as foo
+    WHERE foo.user_id = a_users.user_id
+) bar, users_table as b_users
+WHERE bar.user_id = b_users.user_id
+GROUP BY b_users.value_1;
diff --git a/test_focus_pg18.sql b/test_focus_pg18.sql
new file mode 100644
index 000000000..3d2cf0bef
--- /dev/null
+++ b/test_focus_pg18.sql
@@ -0,0 +1,37 @@
+-- Focus on the ?column? issue specifically
+\c citus
+
+-- Tables should already exist, just in case
+CREATE TABLE IF NOT EXISTS users_table (user_id int, value_1 int, value_2 int);
+CREATE TABLE IF NOT EXISTS events_table (user_id int, event_type int, value_2 int);
+
+-- Populate with minimal data
+INSERT INTO users_table (user_id, value_1, value_2) VALUES (1, 10, 100), (2, 20, 200) ON CONFLICT DO NOTHING;
+INSERT INTO events_table (user_id, event_type, value_2) VALUES (1, 1, 1), (2, 2, 2) ON CONFLICT DO NOTHING;
+
+-- Test the simplified ?column? issue
+SELECT DISTINCT user_id
+FROM (
+    SELECT users_table.user_id 
+    FROM users_table,
+    (
+        SELECT avg(event_type) as avg_val
+        FROM (
+            SELECT event_type, a_users.user_id
+            FROM users_table as a_users, 
+            (
+                SELECT user_id, event_type 
+                FROM events_table 
+                WHERE value_2 < 3 
+                ORDER BY 1, 2 
+                LIMIT 1
+            ) as foo
+            WHERE foo.user_id = a_users.user_id
+        ) bar, users_table as b_users
+        WHERE bar.user_id = b_users.user_id
+        GROUP BY b_users.value_1
+    ) as baz
+    WHERE baz.avg_val < users_table.user_id
+    ORDER BY 1
+    LIMIT 1
+) as sub1;
diff --git a/test_nested_pg18.sql b/test_nested_pg18.sql
new file mode 100644
index 000000000..565c77721
--- /dev/null
+++ b/test_nested_pg18.sql
@@ -0,0 +1,41 @@
+-- Test deeply nested queries with JOINs and GROUP BY
+\c citus
+
+-- Test the exact failing pattern step by step
+-- Step 1: Simple subquery with JOIN (should work)
+SELECT avg(event_type) as avg_val
+FROM (
+    SELECT event_type, users_table.user_id
+    FROM users_table, events_table
+    WHERE events_table.user_id = users_table.user_id
+) sub
+GROUP BY sub.user_id;
+
+-- Step 2: Add one more level of nesting (might fail)
+SELECT avg_val
+FROM (
+    SELECT avg(event_type) as avg_val
+    FROM (
+        SELECT event_type, users_table.user_id
+        FROM users_table, events_table
+        WHERE events_table.user_id = users_table.user_id
+    ) sub
+    GROUP BY sub.user_id
+) outer_sub;
+
+-- Step 3: The exact failing pattern (this should fail)
+SELECT avg(event_type) as avg_val
+FROM (
+    SELECT event_type, a_users.user_id
+    FROM users_table as a_users, 
+    (
+        SELECT user_id, event_type 
+        FROM events_table 
+        WHERE value_2 < 3 
+        ORDER BY 1, 2 
+        LIMIT 1
+    ) as foo
+    WHERE foo.user_id = a_users.user_id
+) bar, users_table as b_users
+WHERE bar.user_id = b_users.user_id
+GROUP BY b_users.value_1;
diff --git a/test_pg18_fix_final.sql b/test_pg18_fix_final.sql
new file mode 100644
index 000000000..36e7e371b
--- /dev/null
+++ b/test_pg18_fix_final.sql
@@ -0,0 +1,30 @@
+-- Test PostgreSQL 18 compatibility using existing distributed tables
+\c citus
+
+-- Test the exact pattern from subqueries_deep.sql that should fail without our fix
+SELECT
+	DISTINCT user_id
+FROM
+	(
+		SELECT users_table.user_id FROM users_table,
+		(
+			SELECT
+				avg(event_type) as avg_val
+			FROM
+				(SELECT
+					event_type, users_table.user_id
+				 FROM
+				 	users_table, (SELECT user_id, event_type FROM events_table WHERE value_2 < 3 ORDER BY 1, 2 OFFSET 0) as foo
+				 WHERE
+				 	foo.user_id = users_table.user_id) bar, users_table
+			WHERE
+				bar.user_id = users_table.user_id
+		GROUP BY
+			users_table.value_1
+		) as baz
+		WHERE
+			baz.avg_val < users_table.user_id
+		ORDER BY 1
+		LIMIT 3
+	) as sub1
+	ORDER BY 1 DESC;
diff --git a/test_simple_pg18.sql b/test_simple_pg18.sql
new file mode 100644
index 000000000..6d0383b4a
--- /dev/null
+++ b/test_simple_pg18.sql
@@ -0,0 +1,26 @@
+-- Simple PostgreSQL 18 test for "?column?" issue
+CREATE SCHEMA test_simple;
+SET search_path TO test_simple;
+
+CREATE TABLE simple_table (
+    id INTEGER,
+    value TEXT
+);
+
+SELECT create_distributed_table('simple_table', 'id');
+
+INSERT INTO simple_table VALUES (1, 'a'), (2, 'b'), (3, 'c');
+
+-- Test a simple subquery that might trigger the "?column?" issue
+SELECT * FROM (
+    SELECT id FROM simple_table 
+) AS sub;
+
+-- Test more complex nested subquery
+SELECT * FROM (
+    SELECT id FROM (
+        SELECT id, value FROM simple_table
+    ) inner_sub
+) outer_sub;
+
+DROP SCHEMA test_simple CASCADE;
diff --git a/test_simple_subquery.sql b/test_simple_subquery.sql
new file mode 100644
index 000000000..13d4f7c59
--- /dev/null
+++ b/test_simple_subquery.sql
@@ -0,0 +1,29 @@
+-- Simple test to isolate the PostgreSQL 18 issue
+-- This should show where the ?column? error occurs
+
+-- Drop and recreate to start fresh
+DROP SCHEMA IF EXISTS simple_test CASCADE;
+CREATE SCHEMA simple_test;
+SET search_path TO simple_test, public;
+
+CREATE TABLE events_table (
+    user_id int,
+    event_type int,
+    value_2 int
+);
+
+SELECT create_distributed_table('events_table', 'user_id');
+
+INSERT INTO events_table VALUES 
+(1, 1, 1),
+(2, 2, 2),
+(3, 3, 3);
+
+SET client_min_messages TO DEBUG1;
+
+-- This is the simplest subquery that should trigger the issue
+SELECT user_id, event_type FROM events_table WHERE value_2 < 3 ORDER BY 1, 2 OFFSET 3;
+
+-- Clean up
+SET search_path TO public;
+DROP SCHEMA simple_test CASCADE;
diff --git a/test_subqueries_deep_custom.sql b/test_subqueries_deep_custom.sql
new file mode 100644
index 000000000..33f4def91
--- /dev/null
+++ b/test_subqueries_deep_custom.sql
@@ -0,0 +1,78 @@
+-- Test PostgreSQL 18 "?column?" fix for subqueries_deep
+-- Create basic tables for testing
+CREATE SCHEMA test_pg18_fix;
+SET search_path TO test_pg18_fix, public;
+
+-- Create test tables similar to what the regular tests use
+CREATE TABLE users_table (
+    user_id int,
+    time timestamp,
+    value_1 int,
+    value_2 int,
+    value_3 double precision,
+    value_4 bigint
+);
+
+CREATE TABLE events_table (
+    user_id int,
+    time timestamp,
+    event_type int,
+    value_2 int,
+    value_3 double precision,
+    value_4 bigint
+);
+
+-- Create distributed tables  
+SELECT create_distributed_table('users_table', 'user_id');
+SELECT create_distributed_table('events_table', 'user_id');
+
+-- Insert some test data
+INSERT INTO users_table VALUES 
+(1, '2024-01-01', 10, 1, 1.1, 100),
+(2, '2024-01-02', 20, 2, 2.2, 200),
+(3, '2024-01-03', 30, 3, 3.3, 300),
+(4, '2024-01-04', 40, 4, 4.4, 400),
+(5, '2024-01-05', 50, 5, 5.5, 500),
+(6, '2024-01-06', 60, 6, 6.6, 600);
+
+INSERT INTO events_table VALUES 
+(1, '2024-01-01', 1, 1, 1.1, 100),
+(2, '2024-01-02', 2, 2, 2.2, 200),
+(3, '2024-01-03', 3, 3, 3.3, 300),
+(4, '2024-01-04', 4, 4, 4.4, 400),
+(5, '2024-01-05', 5, 5, 5.5, 500),
+(6, '2024-01-06', 1, 6, 6.6, 600);
+
+SET client_min_messages TO DEBUG1;
+
+-- Test the original failing query from subqueries_deep.sql
+SELECT
+	DISTINCT user_id
+FROM
+	(
+		SELECT users_table.user_id FROM users_table,
+		(
+			SELECT
+				avg(event_type) as avg_val
+			FROM
+				(SELECT
+					event_type, users_table.user_id
+				 FROM
+				 	users_table, (SELECT user_id, event_type FROM events_table WHERE value_2 < 3 ORDER BY 1, 2 OFFSET 3) as foo
+				 WHERE
+				 	foo.user_id = users_table.user_id) bar, users_table
+			WHERE
+				bar.user_id = users_table.user_id
+		GROUP BY
+			users_table.value_1
+		) as baz
+		WHERE
+			baz.avg_val < users_table.user_id
+		ORDER BY 1
+		LIMIT 3
+	) as sub1
+	ORDER BY 1 DESC;
+
+-- Clean up
+SET search_path TO public;
+DROP SCHEMA test_pg18_fix CASCADE;