A clean-up for c8141f53140054282306d17459310fbca94cbf0e

MDEV-7950 Item_func::type() takes 0.26% in OLTP RO (Step#2)

- Item_ref was doing unnecessary extra job after the "MDEV-7950 Step#2" patch.
  Fallback to Item::build_equal_items() if real_type() is not FIELD_ITEM.
  Note, Item_ref::build_equal_items() will most likely be further simplified.
  Waiting for Sanja and Igor to check a possibly dead code.

- Safety: Adding Item_sum::build_equal_items() with ASSERT, as Item_sum
  should never appear in build_equal_items() context.

1 files changed, 11 insertions, 0 deletions

diff --git a/sql/item_sum.h b/sql/item_sum.h
index db45a336b46..b540b44a31e 100644
--- a/sql/item_sum.h
+++ b/sql/item_sum.h
@@ -444,6 +444,17 @@ public:
   */
   table_map used_tables() const { return used_tables_cache; }
   void update_used_tables ();
+  COND *build_equal_items(THD *thd, COND_EQUAL *inherited,
+                          bool link_item_fields)
+  {
+    /*
+      Item_sum (and derivants) of the original WHERE/HAVING clauses
+      should already be replaced to Item_aggregate_ref by the time when
+      build_equal_items() is called. See Item::split_sum_func2().
+    */
+    DBUG_ASSERT(0);
+    return Item::build_equal_items(thd, inherited, link_item_fields);
+  }
   bool is_null() { return null_value; }
   void make_const () 
   {