Fix bug#13356 resolve_const_item() wasn't able to handle Item_row items.

resolve_const_item() assumed to be not called for Item_row items. For
ensuring that DBUG_ASSERT(0) was set there.

This patch adds section for Item_row items. If it can it recursively calls
resolve_const_item() for each item the Item_row contains. If any of the
contained items is null then whole Item_row substitued by Item_null. Otherwise
it just returns.

mysql-test/r/select.result

@@ -2617,3 +2617,12 @@ select found_rows();
 found_rows()
 1
 DROP TABLE t1;
+create table t1(f1 int, f2 int);
+create table t2(f3 int);
+select f1 from t1,t2 where f1=f2 and (f1,f2) = ((1,1));
+f1
+select f1 from t1,t2 where f1=f2 and (f1,NULL) = ((1,1));
+f1
+select f1 from t1,t2 where f1=f2 and (f1,f2) = ((1,NULL));
+f1
+drop table t1,t2;

mysql-test/t/select.test

@@ -2164,4 +2164,14 @@ select found_rows();
 
 DROP TABLE t1;
 
+#
+# Bug #13356 assertion failed in resolve_const_item()
+#
+create table t1(f1 int, f2 int);
+create table t2(f3 int);
+select f1 from t1,t2 where f1=f2 and (f1,f2) = ((1,1));
+select f1 from t1,t2 where f1=f2 and (f1,NULL) = ((1,1));
+select f1 from t1,t2 where f1=f2 and (f1,f2) = ((1,NULL));
+drop table t1,t2; 
+
 # End of 4.1 tests

sql/item.cc

@@ -2870,6 +2870,35 @@ void resolve_const_item(THD *thd, Item **ref, Item *comp_item)
     new_item= (null_value ? (Item*) new Item_null(name) :
                (Item*) new Item_int(name, result, length));
   }
+  else if (res_type == ROW_RESULT)
+  {
+    new_item= 0;
+    /*
+      If item and comp_item are both Item_rows and have same number of cols
+      then process items in Item_row one by one. If Item_row contain nulls
+      substitute it by Item_null. Otherwise just return.
+    */
+    if (item->result_type() == comp_item->result_type() &&
+        ((Item_row*)item)->cols() == ((Item_row*)comp_item)->cols())
+    {
+      Item_row *item_row= (Item_row*)item,*comp_item_row= (Item_row*)comp_item;
+      if (item_row->null_inside())
+        new_item= (Item*) new Item_null(name);
+      else
+      {
+        int i= item_row->cols() - 1;
+        for (; i >= 0; i--)
+        {
+          if (item_row->maybe_null && item_row->el(i)->is_null())
+          {
+            new_item= (Item*) new Item_null(name);
+            break;
+          }
+          resolve_const_item(thd, item_row->addr(i), comp_item_row->el(i));
+        }
+      }
+    }
+  }
   else
   {						// It must REAL_RESULT
     double result=item->val();