Fix EXISTS with select-list window functions (row-index error)

enginetest/queries/join_queries.go

@@ -863,6 +863,62 @@ on w = 0;`,
 }
 
 var JoinScriptTests = []ScriptTest{
+	{
+		// dolthub/dolt#11421: EXISTS with select-list window (ROW_NUMBER)
+		Name: "EXISTS with select-list window function",
+		SetUpScript: []string{
+			"CREATE TABLE t(id INT PRIMARY KEY, a INT);",
+			"CREATE TABLE u(x INT);",
+			"CREATE TABLE u2(x INT, y INT);",
+			"INSERT INTO t VALUES (1,1),(2,2),(3,3);",
+			"INSERT INTO u VALUES (1),(1),(2);",
+			"INSERT INTO u2 VALUES (1,10),(1,20),(2,30);",
+		},
+		Assertions: []ScriptTestAssertion{
+			{
+				Query: "SELECT id FROM t WHERE EXISTS (SELECT 1 FROM u WHERE u.x = t.a) ORDER BY id",
+				Expected: []sql.Row{
+					{1},
+					{2},
+				},
+			},
+			{
+				Query: "SELECT id FROM t WHERE EXISTS (SELECT ROW_NUMBER() OVER () FROM u WHERE u.x = t.a) ORDER BY id",
+				Expected: []sql.Row{
+					{1},
+					{2},
+				},
+			},
+			{
+				Query: "SELECT id FROM t WHERE NOT EXISTS (SELECT ROW_NUMBER() OVER () FROM u WHERE u.x = t.a) ORDER BY id",
+				Expected: []sql.Row{
+					{3},
+				},
+			},
+			// Multi-window EXISTS bodies (>=2 distinct partition schemes) silently returned wrong
+			// rows on main (1,2,3 / empty) instead of crashing; assert correct existence.
+			{
+				Query: "SELECT id FROM t WHERE EXISTS (SELECT ROW_NUMBER() OVER (PARTITION BY u2.y), RANK() OVER (ORDER BY u2.y) FROM u2 WHERE u2.x = t.a) ORDER BY id",
+				Expected: []sql.Row{
+					{1},
+					{2},
+				},
+			},
+			{
+				Query: "SELECT id FROM t WHERE NOT EXISTS (SELECT ROW_NUMBER() OVER (PARTITION BY u2.y), RANK() OVER (ORDER BY u2.y) FROM u2 WHERE u2.x = t.a) ORDER BY id",
+				Expected: []sql.Row{
+					{3},
+				},
+			},
+			// Uncorrelated NOT EXISTS + window: on main this panics (nil pointer in
+			// sql.EvaluateCondition via existsIter) via the len(joinFilters)==0 path;
+			// patched build correctly returns empty.
+			{
+				Query:    "SELECT id FROM t WHERE NOT EXISTS (SELECT ROW_NUMBER() OVER () FROM u) ORDER BY id",
+				Expected: []sql.Row{},
+			},
+		},
+	},
 	{
 		Name:        "Simple join query",
 		SetUpScript: []string{},

sql/analyzer/unnest_exists_subqueries.go

@@ -106,6 +106,10 @@ func simplifyPartialJoinParents(n sql.Node) (sql.Node, bool) {
 		switch n := ret.(type) {
 		case *plan.Having:
 			return nil, false
+		case *plan.Window:
+			// Window functions are 1:1 row-preserving (empty child -> empty output; see
+			// sql/rowexec/rel_iters.go windowToIter), so stripping cannot change row existence.
+			ret = n.Children()[0]
 		case *plan.Project, *plan.GroupBy, *plan.Sort, *plan.Distinct, *plan.TopN, *plan.Limit:
 			// TODO: In most cases, it's necessary to remove *plan.Limit because child Filter nodes will have been
 			//  hoisted out. But what if Limit.Limit evals to 0? https://github.com/dolthub/dolt/issues/10493