some UNION bug fixes..

sql/sql_select.cc

@@ -144,7 +144,7 @@ static bool add_ref_to_table_cond(THD *thd, JOIN_TAB *join_tab);
 static void init_sum_functions(Item_sum **func);
 static bool update_sum_func(Item_sum **func);
 static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
-			    bool distinct);
+			    bool distinct, const char *message=NullS);
 static void describe_info(THD *thd, const char *info);
 
 /*
@@ -195,6 +195,7 @@ mysql_select(THD *thd,TABLE_LIST *tables,List<Item> &fields,COND *conds,
   Procedure	*procedure;
   List<Item>	all_fields(fields);
   bool		select_distinct;
+  SELECT_LEX *select_lex = &(thd->lex.select_lex);
   DBUG_ENTER("mysql_select");
 
   /* Check that all tables, fields, conds and order are ok */
@@ -350,6 +351,9 @@ mysql_select(THD *thd,TABLE_LIST *tables,List<Item> &fields,COND *conds,
   }
   if (cond_value == Item::COND_FALSE || !thd->select_limit)
   {					/* Impossible cond */
+    if (select_options & SELECT_DESCRIBE && select_lex->next)
+      select_describe(&join,false,false,false,"Impossible WHERE");
+    else 
       error=return_zero_rows(result, tables, fields,
 			     join.tmp_table_param.sum_func_count != 0 && !group,
 			     select_options,"Impossible WHERE",having,
@@ -366,6 +370,9 @@ mysql_select(THD *thd,TABLE_LIST *tables,List<Item> &fields,COND *conds,
     {
       if (res < 0)
       {
+	if (select_options & SELECT_DESCRIBE && select_lex->next)
+	  select_describe(&join,false,false,false,"No matching min/max row");
+	else 
 	  error=return_zero_rows(result, tables, fields, !group,
 				 select_options,"No matching min/max row",
 				 having,procedure);
@@ -374,9 +381,12 @@ mysql_select(THD *thd,TABLE_LIST *tables,List<Item> &fields,COND *conds,
       }
       if (select_options & SELECT_DESCRIBE)
       {
+	if (select_lex->next)
+	  select_describe(&join,false,false,false,"Select tables optimized away");
+	else
 	  describe_info(thd,"Select tables optimized away");
 	delete procedure;
-	DBUG_RETURN(0);
+	DBUG_RETURN(error);
       }
       tables=0;					// All tables resolved
     }
@@ -385,7 +395,12 @@ mysql_select(THD *thd,TABLE_LIST *tables,List<Item> &fields,COND *conds,
   {						// Only test of functions
     error=0;
     if (select_options & SELECT_DESCRIBE)
+    {
+      if (select_lex->next)
+	select_describe(&join,false,false,false,"No tables used");
+      else
 	describe_info(thd,"No tables used");
+    }
     else
     {
       result->send_fields(fields,1);
@@ -463,6 +478,9 @@ mysql_select(THD *thd,TABLE_LIST *tables,List<Item> &fields,COND *conds,
   }
   if (make_join_select(&join,select,conds))
   {
+    if (select_options & SELECT_DESCRIBE && select_lex->next)
+      select_describe(&join,false,false,false,"Impossible WHERE noticed after reading const tables");
+    else 
       error=return_zero_rows(result,tables,fields,
 			     join.tmp_table_param.sum_func_count != 0 && !group,
 			     select_options,
@@ -535,7 +553,7 @@ mysql_select(THD *thd,TABLE_LIST *tables,List<Item> &fields,COND *conds,
   make_join_readinfo(&join,
 		     (select_options & (SELECT_DESCRIBE |
 					SELECT_NO_JOIN_CACHE)) |
-     (thd->lex.select_lex.ftfunc_list.elements ? SELECT_NO_JOIN_CACHE : 0));
+     (select_lex->ftfunc_list.elements ? SELECT_NO_JOIN_CACHE : 0));
 
   /* Need to tell Innobase that to play it safe, it should fetch all
      columns of the tables: this is because MySQL
@@ -2516,6 +2534,7 @@ static void
 make_join_readinfo(JOIN *join,uint options)
 {
   uint i;
+  SELECT_LEX *select_lex = &(join->thd->lex.select_lex);
   DBUG_ENTER("make_join_readinfo");
 
   for (i=join->const_tables ; i < join->tables ; i++)
@@ -2598,7 +2617,7 @@ make_join_readinfo(JOIN *join,uint options)
       /* These init changes read_record */
       if (tab->use_quick == 2)
       {
-	join->thd->lex.select_lex.options|=QUERY_NO_GOOD_INDEX_USED;
+	select_lex->options|=QUERY_NO_GOOD_INDEX_USED;
 	tab->read_first_record= join_init_quick_read_record;
 	statistic_increment(select_range_check_count, &LOCK_status);
       }
@@ -2613,7 +2632,7 @@ make_join_readinfo(JOIN *join,uint options)
 	  }
 	  else
 	  {
-	    join->thd->lex.select_lex.options|=QUERY_NO_INDEX_USED;
+	    select_lex->options|=QUERY_NO_INDEX_USED;
 	    statistic_increment(select_scan_count, &LOCK_status);
 	  }
 	}
@@ -2625,7 +2644,7 @@ make_join_readinfo(JOIN *join,uint options)
 	  }
 	  else
 	  {
-	    join->thd->lex.select_lex.options|=QUERY_NO_INDEX_USED;
+	    select_lex->options|=QUERY_NO_INDEX_USED;
 	    statistic_increment(select_full_join_count, &LOCK_status);
 	  }
 	}
@@ -6940,16 +6959,17 @@ static bool add_ref_to_table_cond(THD *thd, JOIN_TAB *join_tab)
 ****************************************************************************/
 
 static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
-			    bool distinct)
+			    bool distinct,const char *message)
 {
   List<Item> field_list;
   Item *item;
   THD *thd=join->thd;
+  SELECT_LEX *select_lex = &(join->thd->lex.select_lex);
   DBUG_ENTER("select_describe");
 
   /* Don't log this into the slow query log */
-  join->thd->lex.select_lex.options&= ~(QUERY_NO_INDEX_USED | QUERY_NO_GOOD_INDEX_USED);
-  if (join->thd->lex.select == &join->thd->lex.select_lex)
+  select_lex->options&= ~(QUERY_NO_INDEX_USED | QUERY_NO_GOOD_INDEX_USED);
+  if (join->thd->lex.select == select_lex)
   {
     field_list.push_back(new Item_empty_string("table",NAME_LEN));
     field_list.push_back(new Item_empty_string("type",10));
@@ -6970,6 +6990,22 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
   }
   char buff[512],*buff_ptr;
   String tmp(buff,sizeof(buff)),*packet= &thd->packet;
+  if (message)
+  {
+    packet->length(0);
+    net_store_null(packet);
+    net_store_null(packet);
+    net_store_null(packet);
+    net_store_null(packet);
+    net_store_null(packet);
+    net_store_null(packet);
+    net_store_null(packet);
+    net_store_data(packet,message,strlen(message));
+    if (my_net_write(&thd->net,(char*) packet->ptr(),packet->length()))
+      DBUG_VOID_RETURN;
+  }
+  else
+  {
     table_map used_tables=0;
     for (uint i=0 ; i < join->tables ; i++)
     {
@@ -7093,11 +7129,12 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
       }
       net_store_data(packet,buff,(uint) (buff_ptr - buff));
       if (my_net_write(&thd->net,(char*) packet->ptr(),packet->length()))
-      DBUG_VOID_RETURN;				/* purecov: inspected */
+	DBUG_VOID_RETURN;				/* Purecov: Inspected */
 
       // For next iteration
       used_tables|=table->map;
     }
+  }
   if (!join->thd->lex.select->next)
     send_eof(&thd->net);
   DBUG_VOID_RETURN;

sql/sql_union.cc

@@ -76,6 +76,12 @@ int mysql_union(THD *thd, LEX *lex,select_result *result)
     for (sl= &lex->select_lex; sl; sl=sl->next)
     {
       lex->select=sl;
+      thd->offset_limit=sl->offset_limit;
+      thd->select_limit=sl->select_limit+sl->offset_limit;
+      if (thd->select_limit < sl->select_limit)
+	thd->select_limit= HA_POS_ERROR;		// no limit
+      if (thd->select_limit == HA_POS_ERROR)
+	sl->options&= ~OPTION_FOUND_ROWS;
       res=mysql_select(thd, (TABLE_LIST*) sl->table_list.first,
 		       sl->item_list,
 		       sl->where,