fixed union with prepared statement bug found by Konstantin

sql/sql_lex.cc:
  initialisation for safety
sql/sql_union.cc:
  item list should be saved in statement memory
tests/client_test.c:
  test suite

sql/sql_lex.cc

@@ -1004,6 +1004,7 @@ void st_select_lex_unit::init_query()
   table= 0;
   fake_select_lex= 0;
   cleaned= 0;
+  item_list.empty();
 }
 
 void st_select_lex::init_query()

sql/sql_union.cc

@@ -226,14 +226,24 @@ int st_select_lex_unit::prepare(THD *thd_arg, select_result *sel_result,
 
     thd_arg->lex->current_select= lex_select_save;
     {
+      Statement *stmt= thd->current_statement;
+      Statement backup;
+      if (stmt)
+	thd->set_n_backup_item_arena(stmt, &backup);
       Field **field;
       for (field= table->field; *field; field++)
       {
 	Item_field *item= new Item_field(*field);
 	if (!item || item_list.push_back(item))
+	{
+	  if (stmt)
+	    thd->restore_backup_item_arena(stmt, &backup);
 	  DBUG_RETURN(-1);
 	}
       }
+      if (stmt)
+	thd->restore_backup_item_arena(stmt, &backup);
+    }
   }
   else
     first_select->braces= 0; // remove our changes
@@ -427,7 +437,7 @@ int st_select_lex_unit::cleanup()
   {
     DBUG_RETURN(0);
   }
-  cleaned= 0;
+  cleaned= 1;
 
   if (union_result)
   {
@@ -461,9 +471,11 @@ void st_select_lex_unit::reinit_exec_mechanism()
 {
   prepared= optimized= executed= 0;
 #ifndef DBUG_OFF
+  if (first_select()->next_select())
+  {
     List_iterator_fast<Item> it(item_list);
-  Item_field *field;
-  while ((field= (Item_field *)it++))
+    Item *field;
+    while ((field= it++))
     {
       /*
 	we can't cleanup here, because it broke link to temporary table field,
@@ -472,5 +484,6 @@ void st_select_lex_unit::reinit_exec_mechanism()
       */
       field->fixed= 0;
     }
+  }
 #endif
 }

tests/client_test.c

@@ -160,7 +160,10 @@ static void print_st_error(MYSQL_STMT *stmt, const char *msg)
 MYSQL_STMT *STDCALL
 mysql_simple_prepare(MYSQL  *mysql, const char *query)
 {
-  return mysql_prepare(mysql, query, strlen(query));
+  MYSQL_STMT *stmt= mysql_stmt_init(mysql);
+  if (mysql_stmt_prepare(stmt, query, strlen(query)))
+    return 0;
+  return stmt;
 }
 
 
@@ -8377,6 +8380,58 @@ static void test_subqueries_ref()
   myquery(rc);
 }
 
+
+static void test_union()
+{
+  MYSQL_STMT *stmt;
+  int rc;
+
+  myheader("test_union");
+ 
+  rc= mysql_query(mysql, "DROP TABLE IF EXISTS t1, t2");
+  myquery(rc);
+
+  rc= mysql_query(mysql,
+                  "CREATE TABLE t1 "
+                  "(id INTEGER NOT NULL PRIMARY KEY, "
+                  " name VARCHAR(20) NOT NULL)");
+  myquery(rc);
+  rc= mysql_query(mysql,
+                  "INSERT INTO t1 (id, name) VALUES "
+                  "(2, 'Ja'), (3, 'Ede'), "
+                  "(4, 'Haag'), (5, 'Kabul'), "
+                  "(6, 'Almere'), (7, 'Utrecht'), "
+                  "(8, 'Qandahar'), (9, 'Amsterdam'), "
+                  "(10, 'Amersfoort'), (11, 'Constantine')");
+  myquery(rc);
+  rc= mysql_query(mysql,
+                  "CREATE TABLE t2 "
+                  "(id INTEGER NOT NULL PRIMARY KEY, "
+                  " name VARCHAR(20) NOT NULL)");
+  myquery(rc);
+  rc= mysql_query(mysql,
+                  "INSERT INTO t2 (id, name) VALUES "
+                  "(4, 'Guam'), (5, 'Aruba'), "
+                  "(6, 'Angola'), (7, 'Albania'), "
+                  "(8, 'Anguilla'), (9, 'Argentina'), "
+                  "(10, 'Azerbaijan'), (11, 'Afghanistan'), "
+                  "(12, 'Burkina Faso'), (13, 'Faroe Islands')");
+  myquery(rc);
+ 
+  stmt= mysql_simple_prepare(mysql,
+                             "SELECT t1.name FROM t1 UNION "
+                             "SELECT t2.name FROM t2");
+  mystmt_init(stmt);
+
+  rc= mysql_stmt_execute(stmt);
+  mystmt(stmt,rc);
+  assert(20 == my_process_stmt_result(stmt));
+  mysql_stmt_close(stmt);
+
+  rc= mysql_query(mysql, "DROP TABLE t1, t2");
+  myquery(rc);
+}
+
 /*
   Read and parse arguments and MySQL options from my.cnf
 */
@@ -8634,8 +8689,7 @@ int main(int argc, char **argv)
     test_distinct();	    /* distinct aggregate functions */
     test_subqueries_ref();  /* outer reference in subqueries converted
 			       Item_field -> Item_ref */
-
-
+    test_union();	    /* test union with prepared statements */
 
     end_time= time((time_t *)0);
     total_time+= difftime(end_time, start_time);