test of duplicate field names (BUG#4608)

mysql-test/r/view.result:
  test of duplicate field names
mysql-test/t/view.test:
  test of duplicate field names
sql/sql_view.cc:
  test of duplicate field names

mysql-test/r/view.result

@@ -975,3 +975,5 @@ drop table t1;
 select * from v1;
 ERROR HY000: View 'test.v1' references invalid table(s) or column(s)
 drop view v1;
+create view v1 (a,a) as select 'a','a';
+ERROR 42S21: Duplicate column name 'a'

mysql-test/t/view.test

@@ -894,3 +894,9 @@ drop table t1;
 -- error 1354
 select * from v1;
 drop view v1;
+
+#
+# check of duplication of column names
+#
+-- error 1060
+create view v1 (a,a) as select 'a','a';

sql/sql_view.cc

@@ -204,6 +204,26 @@ int mysql_create_view(THD *thd,
     }
   }
 
+  /* Test absence of duplicates names */
+  {
+    Item *item;
+    List_iterator_fast<Item> it(select_lex->item_list);
+    it++;
+    while((item= it++))
+    {
+      Item *check;
+      List_iterator_fast<Item> itc(select_lex->item_list);
+      while((check= itc++) && check != item)
+      {
+        if (strcmp(item->name, check->name) == 0)
+        {
+          my_error(ER_DUP_FIELDNAME, MYF(0), item->name);
+          DBUG_RETURN(-1);
+        }
+      }
+    }
+  }
+
 #ifndef NO_EMBEDDED_ACCESS_CHECKS
   /*
     Compare/check grants on view with grants of underlaying tables