MDEV-20200: AddressSanitizer: use-after-poison in Item_direct_view_ref::get_null_ref_table

Do not cast wrong type.

mysql-test/main/having.result

@@ -864,4 +864,13 @@ x
 Warnings:
 Warning	1292	Truncated incorrect DOUBLE value: 'x'
 DROP TABLE t1,t2;
+#
+# MDEV-20200: AddressSanitizer: use-after-poison in
+# Item_direct_view_ref::get_null_ref_table
+#
+CREATE TABLE t (f VARCHAR(512));
+INSERT INTO t VALUES ('a'),('b');
+SELECT * FROM t HAVING f = 'foo';
+f
+DROP TABLE t;
 # End of 10.4 tests

mysql-test/main/having.test

@@ -909,4 +909,17 @@ HAVING t.f != 112 AND t.f = 'x' AND t.f != 'a';
 
 DROP TABLE t1,t2;
 
+
+--echo #
+--echo # MDEV-20200: AddressSanitizer: use-after-poison in
+--echo # Item_direct_view_ref::get_null_ref_table
+--echo #
+
+CREATE TABLE t (f VARCHAR(512));
+INSERT INTO t VALUES ('a'),('b');
+SELECT * FROM t HAVING f = 'foo';
+
+# Cleanup
+DROP TABLE t;
+
 --echo # End of 10.4 tests

sql/sql_select.cc

@@ -14333,27 +14333,38 @@ bool check_simple_equality(THD *thd, const Item::Context &ctx,
 {
   Item *orig_left_item= left_item;
   Item *orig_right_item= right_item;
-  if (left_item->type() == Item::REF_ITEM &&
-      (((Item_ref*)left_item)->ref_type() == Item_ref::VIEW_REF ||
-      ((Item_ref*)left_item)->ref_type() == Item_ref::REF))
+  if (left_item->type() == Item::REF_ITEM)
   {
-    if (((Item_ref*)left_item)->get_depended_from())
-      return FALSE;
-    if (((Item_direct_view_ref*)left_item)->get_null_ref_table() !=
-        NO_NULL_TABLE && !left_item->real_item()->used_tables())
-      return FALSE;
-    left_item= left_item->real_item();
+    Item_ref::Ref_Type left_ref= ((Item_ref*)left_item)->ref_type();
+
+    if (left_ref == Item_ref::VIEW_REF ||
+        left_ref == Item_ref::REF)
+    {
+      if (((Item_ref*)left_item)->get_depended_from())
+        return FALSE;
+      if (left_ref == Item_ref::VIEW_REF &&
+          ((Item_direct_view_ref*)left_item)->get_null_ref_table() !=
+           NO_NULL_TABLE &&
+          !left_item->real_item()->used_tables())
+        return FALSE;
+      left_item= left_item->real_item();
+    }
   }
-  if (right_item->type() == Item::REF_ITEM &&
-      (((Item_ref*)right_item)->ref_type() == Item_ref::VIEW_REF ||
-      ((Item_ref*)right_item)->ref_type() == Item_ref::REF))
+  if (right_item->type() == Item::REF_ITEM)
   {
-    if (((Item_ref*)right_item)->get_depended_from())
-      return FALSE;
-    if (((Item_direct_view_ref*)right_item)->get_null_ref_table() !=
-        NO_NULL_TABLE && !right_item->real_item()->used_tables())
-      return FALSE;
-    right_item= right_item->real_item();
+    Item_ref::Ref_Type right_ref= ((Item_ref*)right_item)->ref_type();
+    if (right_ref == Item_ref::VIEW_REF ||
+       (right_ref == Item_ref::REF))
+    {
+      if (((Item_ref*)right_item)->get_depended_from())
+        return FALSE;
+      if (right_ref == Item_ref::VIEW_REF &&
+          ((Item_direct_view_ref*)right_item)->get_null_ref_table() !=
+           NO_NULL_TABLE &&
+          !right_item->real_item()->used_tables())
+        return FALSE;
+      right_item= right_item->real_item();
+    }
   }
   if (left_item->type() == Item::FIELD_ITEM &&
       right_item->type() == Item::FIELD_ITEM &&