Fixed bug #18386.

An invalid assertion in Item_direct_view_ref::eq caused 
an assertion abort in the debug version.

mysql-test/r/view.result

@@ -2553,3 +2553,12 @@ a	b
 3	3
 drop view v2, v1;
 drop table t1;
+CREATE TABLE t1 (a int);
+INSERT INTO t1 VALUES (1), (2);
+CREATE VIEW v1 AS SELECT SQRT(a) my_sqrt FROM t1;
+SELECT my_sqrt FROM v1 ORDER BY my_sqrt;
+my_sqrt
+1
+1.4142135623731
+DROP VIEW v1;
+DROP TABLE t1;

mysql-test/t/view.test

@@ -2399,3 +2399,17 @@ update v2 set b=3 where a=2;
 select * from v2;
 drop view v2, v1;
 drop table t1;
+
+#
+# Bug #18386: select from view over a table with ORDER BY view_col clause 
+#             given view_col is not an image of any column from the base table
+
+CREATE TABLE t1 (a int);
+INSERT INTO t1 VALUES (1), (2);
+
+CREATE VIEW v1 AS SELECT SQRT(a) my_sqrt FROM t1;
+
+SELECT my_sqrt FROM v1 ORDER BY my_sqrt;
+
+DROP VIEW v1;
+DROP TABLE t1;

sql/item.cc

@@ -5076,11 +5076,8 @@ bool Item_direct_view_ref::fix_fields(THD *thd, Item **reference)
   DESCRIPTION
     A view column reference is considered equal to another column
     reference if the second one is a view column and if both column
-    references point to the same field. For views 'same field' means
-    the same Item_field object in the view translation table, where
-    the view translation table contains all result columns of the
-    view. This definition ensures that view columns are resolved
-    in the same manner as table columns.
+    references resolve to the same item. It is assumed that both
+    items are of the same type.
 
   RETURN
     TRUE    Referenced item is equal to given item
@@ -5096,8 +5093,8 @@ bool Item_direct_view_ref::eq(const Item *item, bool binary_cmp) const
     if (item_ref->ref_type() == VIEW_REF)
     {
       Item *item_ref_ref= *(item_ref->ref);
-      DBUG_ASSERT((*ref)->real_item()->type() == FIELD_ITEM &&
-                  (item_ref_ref->real_item()->type() == FIELD_ITEM));
+      DBUG_ASSERT((*ref)->real_item()->type() == 
+                  item_ref_ref->real_item()->type());
       return ((*ref)->real_item() == item_ref_ref->real_item());
     }
   }