item.h:

  Revised the fix for bug #7098.
  Corrected the method Item_string::new_item.
sql_select.cc:
  Revised the fix for bug #7098.
  Aborted the previous modifications.

sql/item.h

@@ -742,7 +742,7 @@ class Item_string :public Item
   Item *new_item() 
   {
     return new Item_string(name, str_value.ptr(), 
-    			   str_value.length(), &my_charset_bin);
+    			   str_value.length(), collation.collation);
   }
   Item *safe_charset_converter(CHARSET_INFO *tocs);
   String *const_string() { return &str_value; }

sql/sql_select.cc

@@ -4230,8 +4230,6 @@ change_cond_ref_to_const(THD *thd, I_List<COND_CMP> *save_list,
     Item *tmp=value->new_item();
     if (tmp)
     {
-      tmp->collation.set(value->collation.collation,
-                         value->collation.derivation);
       thd->change_item_tree(args + 1, tmp);
       func->update_used_tables();
       if ((functype == Item_func::EQ_FUNC || functype == Item_func::EQUAL_FUNC)
@@ -4253,8 +4251,6 @@ change_cond_ref_to_const(THD *thd, I_List<COND_CMP> *save_list,
     Item *tmp=value->new_item();
     if (tmp)
     {
-      tmp->collation.set(value->collation.collation,
-                         value->collation.derivation);
       thd->change_item_tree(args, tmp);
       value= tmp;
       func->update_used_tables();