Fixed bug #18237.

The code in opt_sum_query that prevented the COUNT/MIN/MAX 
optimization from being applied to outer joins  was not adjusted 
after introducing nested joins. As a result if an outer join
contained a reference to a view as an inner table the code of
opt_sum_query missed the presence of an on expressions and
erroneously applied the mentioned optimization.

mysql-test/r/view.result

@@ -2562,3 +2562,20 @@ my_sqrt
 1.4142135623731
 DROP VIEW v1;
 DROP TABLE t1;
+CREATE TABLE t1 (id int PRIMARY KEY);
+CREATE TABLE t2 (id int PRIMARY KEY);
+INSERT INTO t1 VALUES (1), (3);
+INSERT INTO t2 VALUES (1), (2), (3);
+CREATE VIEW v2 AS SELECT * FROM t2;
+SELECT COUNT(*) FROM t1 LEFT JOIN t2 ON t1.id=t2.id;
+COUNT(*)
+2
+SELECT * FROM t1 LEFT JOIN t2 ON t1.id=t2.id;
+id	id
+1	1
+3	3
+SELECT COUNT(*) FROM t1 LEFT JOIN v2 ON t1.id=v2.id;
+COUNT(*)
+2
+DROP VIEW v2;
+DROP TABLE t1, t2;

mysql-test/t/view.test

@@ -2413,3 +2413,24 @@ SELECT my_sqrt FROM v1 ORDER BY my_sqrt;
 
 DROP VIEW v1;
 DROP TABLE t1;
+
+#
+# Bug #18237: invalid count optimization applied to an outer join with a view 
+#             
+
+CREATE TABLE t1 (id int PRIMARY KEY);
+CREATE TABLE t2 (id int PRIMARY KEY);
+
+INSERT INTO t1 VALUES (1), (3);
+INSERT INTO t2 VALUES (1), (2), (3);
+
+CREATE VIEW v2 AS SELECT * FROM t2;
+
+SELECT COUNT(*) FROM t1 LEFT JOIN t2 ON t1.id=t2.id;
+SELECT * FROM t1 LEFT JOIN t2 ON t1.id=t2.id;
+
+SELECT COUNT(*) FROM t1 LEFT JOIN v2 ON t1.id=v2.id;
+
+DROP VIEW v2;
+
+DROP TABLE t1, t2;

sql/opt_sum.cc

@@ -96,8 +96,14 @@ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds)
   */
   for (TABLE_LIST *tl= tables; tl; tl= tl->next_leaf)
   {
+    TABLE_LIST *embedded;
+    for (embedded= tl ; embedded; embedded= embedded->embedding)
+    {
+      if (embedded->on_expr)
+        break;
+    }
+    if (embedded)
     /* Don't replace expression on a table that is part of an outer join */
-    if (tl->on_expr)
     {
       outer_tables|= tl->table->map;