Fixed bug mdev-12015.

Corrected an assertion in JOIN::create_postjoin_aggr_table():
JOIN::join_tab[0] can be the first aggregation table if
the query uses window functions.

mysql-test/r/win.result

@@ -2842,3 +2842,14 @@ max(i)	min(i)	f
 16	14	2
 20	17	3
 drop table t1;
+#
+# MDEV-12015: window function over select with WHERE  
+#             that is always FALSE
+#
+CREATE TABLE t1 (i INT);
+INSERT INTO t1 VALUES (3), (1), (2);
+SELECT i, ROW_NUMBER() OVER () FROM t1 WHERE 1 = 2;
+i	ROW_NUMBER() OVER ()
+SELECT i, COUNT(*) OVER () FROM t1 WHERE 1 = 2;
+i	COUNT(*) OVER ()
+DROP TABLE t1;

mysql-test/t/win.test

@@ -1636,3 +1636,18 @@ select max(i), min(i), min(max(i)-min(i)) over (partition by count(i)) f
 group by b;
 
 drop table t1;
+
+--echo #
+--echo # MDEV-12015: window function over select with WHERE  
+--echo #             that is always FALSE
+--echo #
+
+CREATE TABLE t1 (i INT);
+INSERT INTO t1 VALUES (3), (1), (2);
+
+SELECT i, ROW_NUMBER() OVER () FROM t1 WHERE 1 = 2;
+
+SELECT i, COUNT(*) OVER () FROM t1 WHERE 1 = 2;
+
+DROP TABLE t1;
+

sql/sql_select.cc

@@ -2779,8 +2779,8 @@ JOIN::create_postjoin_aggr_table(JOIN_TAB *tab, List<Item> *table_fields,
   tmp_table_param.using_outer_summary_function=
     tab->tmp_table_param->using_outer_summary_function;
   tab->join= this;
-  DBUG_ASSERT(tab > tab->join->join_tab || !tables_list);
-  if (tables_list)
+  DBUG_ASSERT(tab > join_tab || select_lex->have_window_funcs());
+  if (tab > join_tab)
     (tab - 1)->next_select= sub_select_postjoin_aggr;
   tab->aggr= new (thd->mem_root) AGGR_OP(tab);
   if (!tab->aggr)