diff --git a/mysql-test/r/win.result b/mysql-test/r/win.result
index 2fe511d0e8b..9e551dd6dd6 100644
--- a/mysql-test/r/win.result
+++ b/mysql-test/r/win.result
@@ -3653,5 +3653,76 @@ COUNT(*) OVER ()	MOD(MIN(i),2)
 3	1
 drop table t1;
 #
+# MDEV-21318: Wrong results with window functions and implicit grouping
+#
+CREATE TABLE t1 (a INT);
+#
+#  With empty const table
+#  The expected result here is 1, NULL
+#
+explain
+SELECT row_number() over(), sum(1) FROM t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	system	NULL	NULL	NULL	NULL	0	const row not found; Using temporary
+SELECT row_number() over(), sum(1) FROM t1;
+row_number() over()	sum(1)
+1	NULL
+insert into t1 values (2);
+#
+#  Const table has 1 row, but still impossible where
+#  The expected result here is 1, NULL
+#
+EXPLAIN SELECT row_number() over(), sum(1) FROM t1 where a=1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+SELECT row_number() over(), sum(1) FROM t1 where a=1;
+row_number() over()	sum(1)
+1	NULL
+#
+#  Impossible HAVING
+#  Empty result is expected
+#
+EXPLAIN SELECT row_number() over(), sum(1) FROM t1 where a=1 having 1=0;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible HAVING
+SELECT row_number() over(), sum(1) FROM t1 where a=1 having 1=0;
+row_number() over()	sum(1)
+#
+#  const table has 1 row, no impossible where
+#  The expected result here is 1, 2
+#
+EXPLAIN SELECT row_number() over(), sum(a) FROM t1 where a=2;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	system	NULL	NULL	NULL	NULL	1	Using temporary
+SELECT row_number() over(), sum(a) FROM t1 where a=2;
+row_number() over()	sum(a)
+1	2
+drop table t1;
+#
+# Impossible Where
+#
+create table t1(a int);
+insert into t1 values (1);
+#
+# Expected result is NULL, 0, NULL
+#
+EXPLAIN SELECT MAX(a) OVER (), COUNT(a), abs(a)  FROM t1 WHERE FALSE;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+SELECT MAX(a) OVER (), COUNT(a), abs(a)  FROM t1 WHERE FALSE;
+MAX(a) OVER ()	COUNT(a)	abs(a)
+NULL	0	NULL
+#
+# Expected result is 1, 0, NULL
+#
+EXPLAIN
+SELECT MAX(1) OVER (), COUNT(a), abs(a)  FROM t1 WHERE FALSE;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+SELECT MAX(1) OVER (), COUNT(a), abs(a)  FROM t1 WHERE FALSE;
+MAX(1) OVER ()	COUNT(a)	abs(a)
+1	0	NULL
+drop table t1;
+#
 # End of 10.2 tests
 #
diff --git a/mysql-test/t/win.test b/mysql-test/t/win.test
index 1e302722b99..d2c0c1c9712 100644
--- a/mysql-test/t/win.test
+++ b/mysql-test/t/win.test
@@ -2361,6 +2361,71 @@ INSERT INTO t1 VALUES (1),(0),(1),(2),(0),(1),(2),(1),(2);
 SELECT  DISTINCT COUNT(*) OVER (), MOD(MIN(i),2) FROM t1 GROUP BY i ;
 drop table t1;
 
+--echo #
+--echo # MDEV-21318: Wrong results with window functions and implicit grouping
+--echo #
+
+CREATE TABLE t1 (a INT);
+
+--echo #
+--echo #  With empty const table
+--echo #  The expected result here is 1, NULL
+--echo #
+
+explain
+SELECT row_number() over(), sum(1) FROM t1;
+SELECT row_number() over(), sum(1) FROM t1;
+
+insert into t1 values (2);
+
+--echo #
+--echo #  Const table has 1 row, but still impossible where
+--echo #  The expected result here is 1, NULL
+--echo #
+
+EXPLAIN SELECT row_number() over(), sum(1) FROM t1 where a=1;
+SELECT row_number() over(), sum(1) FROM t1 where a=1;
+
+--echo #
+--echo #  Impossible HAVING
+--echo #  Empty result is expected
+--echo #
+
+EXPLAIN SELECT row_number() over(), sum(1) FROM t1 where a=1 having 1=0;
+SELECT row_number() over(), sum(1) FROM t1 where a=1 having 1=0;
+
+--echo #
+--echo #  const table has 1 row, no impossible where
+--echo #  The expected result here is 1, 2
+--echo #
+
+EXPLAIN SELECT row_number() over(), sum(a) FROM t1 where a=2;
+SELECT row_number() over(), sum(a) FROM t1 where a=2;
+drop table t1;
+
+--echo #
+--echo # Impossible Where
+--echo #
+
+create table t1(a int);
+insert into t1 values (1);
+
+--echo #
+--echo # Expected result is NULL, 0, NULL
+--echo #
+EXPLAIN SELECT MAX(a) OVER (), COUNT(a), abs(a)  FROM t1 WHERE FALSE;
+SELECT MAX(a) OVER (), COUNT(a), abs(a)  FROM t1 WHERE FALSE;
+
+--echo #
+--echo # Expected result is 1, 0, NULL
+--echo #
+
+EXPLAIN
+SELECT MAX(1) OVER (), COUNT(a), abs(a)  FROM t1 WHERE FALSE;
+SELECT MAX(1) OVER (), COUNT(a), abs(a)  FROM t1 WHERE FALSE;
+
+drop table t1;
+
 --echo #
 --echo # End of 10.2 tests
 --echo #
diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index 1bf8addbcf0..72c1e876359 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -1447,6 +1447,7 @@ JOIN::optimize_inner()
         zero_result_cause= "Zero limit";
       }
       table_count= top_join_tab_count= 0;
+      handle_implicit_grouping_with_window_funcs();
       error= 0;
       goto setup_subq_exit;
     }
@@ -1502,6 +1503,7 @@ JOIN::optimize_inner()
 	zero_result_cause= "No matching min/max row";
         table_count= top_join_tab_count= 0;
 	error=0;
+        handle_implicit_grouping_with_window_funcs();
         goto setup_subq_exit;
       }
       if (res > 1)
@@ -1517,6 +1519,7 @@ JOIN::optimize_inner()
       tables_list= 0;				// All tables resolved
       select_lex->min_max_opt_list.empty();
       const_tables= top_join_tab_count= table_count;
+      handle_implicit_grouping_with_window_funcs();
       /*
         Extract all table-independent conditions and replace the WHERE
         clause with them. All other conditions were computed by opt_sum_query
@@ -1615,6 +1618,7 @@ JOIN::optimize_inner()
     zero_result_cause= "no matching row in const table";
     DBUG_PRINT("error",("Error: %s", zero_result_cause));
     error= 0;
+    handle_implicit_grouping_with_window_funcs();
     goto setup_subq_exit;
   }
   if (!(thd->variables.option_bits & OPTION_BIG_SELECTS) &&
@@ -1639,6 +1643,7 @@ JOIN::optimize_inner()
     zero_result_cause=
       "Impossible WHERE noticed after reading const tables";
     select_lex->mark_const_derived(zero_result_cause);
+    handle_implicit_grouping_with_window_funcs();
     goto setup_subq_exit;
   }
 
@@ -1781,6 +1786,7 @@ JOIN::optimize_inner()
     zero_result_cause=
       "Impossible WHERE noticed after reading const tables";
     select_lex->mark_const_derived(zero_result_cause);
+    handle_implicit_grouping_with_window_funcs();
     goto setup_subq_exit;
   }
 
@@ -18225,7 +18231,8 @@ void set_postjoin_aggr_write_func(JOIN_TAB *tab)
     }
   }
   else if (join->sort_and_group && !tmp_tbl->precomputed_group_by &&
-           !join->sort_and_group_aggr_tab && join->tables_list)
+           !join->sort_and_group_aggr_tab && join->tables_list &&
+           join->top_join_tab_count)
   {
     DBUG_PRINT("info",("Using end_write_group"));
     aggr->set_write_func(end_write_group);
@@ -26925,6 +26932,28 @@ Item *remove_pushed_top_conjuncts(THD *thd, Item *cond)
   return cond;
 }
 
+/*
+  There are 5 cases in which we shortcut the join optimization process as we
+  conclude that the join would be a degenerate one
+    1) IMPOSSIBLE WHERE
+    2) MIN/MAX optimization (@see opt_sum_query)
+    3) EMPTY CONST TABLE
+  If a window function is present in any of the above cases then to get the
+  result of the window function, we need to execute it. So we need to
+  create a temporary table for its execution. Here we need to take in mind
+  that aggregate functions and non-aggregate function need not be executed.
+
+*/
+
+
+void JOIN::handle_implicit_grouping_with_window_funcs()
+{
+  if (select_lex->have_window_funcs() && send_row_on_empty_set())
+  {
+    const_tables= top_join_tab_count= table_count= 0;
+  }
+}
+
 /**
   @} (end of group Query_Optimizer)
 */
diff --git a/sql/sql_select.h b/sql/sql_select.h
index fe44f448446..ffc9eba1186 100644
--- a/sql/sql_select.h
+++ b/sql/sql_select.h
@@ -1057,6 +1057,7 @@ protected:
   void restore_query_plan(Join_plan_state *restore_from);
   /* Choose a subquery plan for a table-less subquery. */
   bool choose_tableless_subquery_plan();
+  void handle_implicit_grouping_with_window_funcs();
 
 public:
   JOIN_TAB *join_tab, **best_ref;