after review changes

mysql-test/r/derived.result:
  explain of hidden subselect changed according to review
mysql-test/r/subselect.result:
  explain of hidden subselect changed according to review
mysql-test/r/union.result:
  explain of hidden subselect changed according to review
sql/sql_class.h:
  we bo not need sign for now
sql/sql_lex.h:
  we do not need sign for now

mysql-test/r/derived.result

@@ -94,13 +94,13 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	<derived2>	ALL	NULL	NULL	NULL	NULL	3	
 2	DERIVED	t1	ALL	NULL	NULL	NULL	NULL	4	
 3	UNION	t1	ALL	NULL	NULL	NULL	NULL	4	
--2	UNION RESULT	<union2>	ALL	NULL	NULL	NULL	NULL	NULL	
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
 explain select * from (select * from t1 union all select * from t1) a;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	<derived2>	ALL	NULL	NULL	NULL	NULL	8	
 2	DERIVED	t1	ALL	NULL	NULL	NULL	NULL	4	
 3	UNION	t1	ALL	NULL	NULL	NULL	NULL	4	
--2	UNION RESULT	<union2>	ALL	NULL	NULL	NULL	NULL	NULL	
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
 CREATE TABLE t2 (a int not null);
 insert into t2 values(1);
 select * from (select * from t1 where t1.a=(select a from t2 where t2.a=t1.a)) a;
@@ -248,10 +248,10 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	<derived4>	ALL	NULL	NULL	NULL	NULL	2	
 4	DERIVED	t1	ALL	NULL	NULL	NULL	NULL	2	
 5	UNION	t1	ALL	NULL	NULL	NULL	NULL	2	
--4	UNION RESULT	<union4>	ALL	NULL	NULL	NULL	NULL	NULL	
+NULL	UNION RESULT	<union4,5>	ALL	NULL	NULL	NULL	NULL	NULL	
 2	DERIVED	t1	ALL	NULL	NULL	NULL	NULL	2	
 3	UNION	t1	ALL	NULL	NULL	NULL	NULL	2	
--2	UNION RESULT	<union2>	ALL	NULL	NULL	NULL	NULL	NULL	
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
 drop table t1;
 CREATE TABLE `t1` (
 `N` int(11) unsigned NOT NULL default '0',

mysql-test/r/subselect.result

@@ -16,7 +16,7 @@ explain extended SELECT (SELECT 1) UNION SELECT (SELECT 2);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
 3	UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
--1	UNION RESULT	<union1>	ALL	NULL	NULL	NULL	NULL	NULL	
+NULL	UNION RESULT	<union1,3>	ALL	NULL	NULL	NULL	NULL	NULL	
 Warnings:
 Note	1249	Select 2 was reduced during optimisation
 Note	1249	Select 4 was reduced during optimisation
@@ -29,7 +29,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
 3	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
 4	UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
--3	UNION RESULT	<union3>	ALL	NULL	NULL	NULL	NULL	NULL	
+NULL	UNION RESULT	<union3,4>	ALL	NULL	NULL	NULL	NULL	NULL	
 Warnings:
 Note	1249	Select 2 was reduced during optimisation
 Note	1003	select (select 0 AS `0` union select 0 AS `0`) AS `(SELECT (SELECT 0 UNION SELECT 0))`
@@ -184,7 +184,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 2	SUBQUERY	t3	ALL	NULL	NULL	NULL	NULL	3	Using filesort
 3	UNION	t4	ALL	NULL	NULL	NULL	NULL	3	Using where; Using filesort
 4	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	2	
--1	UNION RESULT	<union1>	ALL	NULL	NULL	NULL	NULL	NULL	
+NULL	UNION RESULT	<union1,3>	ALL	NULL	NULL	NULL	NULL	NULL	
 Warnings:
 Note	1003	(select test.t2.a AS `a`,test.t2.b AS `b` from test.t2 where (test.t2.b = (select test.t3.a AS `a` from test.t3 order by test.t3.a desc limit 1))) union (select test.t4.a AS `a`,test.t4.b AS `b` from test.t4 where (test.t4.b = (select (max(test.t2.a) * 4) AS `max(t2.a)*4` from test.t2)) order by test.t4.a)
 select (select a from t3 where a<t2.a*4 order by 1 desc limit 1), a from t2;
@@ -309,7 +309,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	2	
 2	DEPENDENT SUBQUERY	t1	system	NULL	NULL	NULL	NULL	1	
 3	DEPENDENT UNION	t5	ALL	NULL	NULL	NULL	NULL	2	Using where
--2	UNION RESULT	<union2>	ALL	NULL	NULL	NULL	NULL	NULL	
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
 Warnings:
 Note	1276	Field or reference 't2.a' of SELECT #2 was resolved in SELECT #1
 Note	1276	Field or reference 't2.a' of SELECT #3 was resolved in SELECT #1
@@ -417,7 +417,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	index	NULL	topic	3	NULL	2	Using index
 2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
 3	UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
--2	UNION RESULT	<union2>	ALL	NULL	NULL	NULL	NULL	NULL	
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
 Warnings:
 Note	1003	select 1 AS `1` from test.t1
 drop table t1;
@@ -732,7 +732,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t2	index	NULL	id	5	NULL	2	Using where; Using index
 2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
 3	DEPENDENT UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
--2	UNION RESULT	<union2>	ALL	NULL	NULL	NULL	NULL	NULL	
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
 Warnings:
 Note	1003	select test.t2.id AS `id` from test.t2 where <in_optimizer>(test.t2.id,<exists>(select 1 AS `Not_used` having (<cache>(test.t2.id) = <null_helper>(1)) union select 1 AS `Not_used` having (<cache>(test.t2.id) = <null_helper>(3))))
 SELECT * FROM t2 WHERE id IN (SELECT 5 UNION SELECT 3);
@@ -1547,7 +1547,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	system	NULL	NULL	NULL	NULL	1	
 2	SUBQUERY	t1	system	NULL	NULL	NULL	NULL	1	
 3	UNION	t1	system	NULL	NULL	NULL	NULL	1	
--2	UNION RESULT	<union2>	ALL	NULL	NULL	NULL	NULL	NULL	
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
 Warnings:
 Note	1003	select test.t1.s1 AS `s1` from test.t1
 drop table t1;

mysql-test/r/union.result

@@ -86,7 +86,7 @@ explain extended (select a,b from t1 limit 2)  union all (select a,b from t2 ord
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	4	
 2	UNION	t2	ALL	NULL	NULL	NULL	NULL	4	Using filesort
--1	UNION RESULT	<union1>	ALL	NULL	NULL	NULL	NULL	NULL	Using filesort
+NULL	UNION RESULT	<union1,2>	ALL	NULL	NULL	NULL	NULL	NULL	Using filesort
 Warnings:
 Note	1003	(select test.t1.a AS `a`,test.t1.b AS `b` from test.t1 limit 2) union all (select test.t2.a AS `a`,test.t2.b AS `b` from test.t2 order by test.t2.a limit 1) order by b desc
 (select sql_calc_found_rows  a,b from t1 limit 2)  union all (select a,b from t2 order by a) limit 2;
@@ -107,7 +107,7 @@ explain select a,b from t1 union all select a,b from t2;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	4	
 2	UNION	t2	ALL	NULL	NULL	NULL	NULL	4	
--1	UNION RESULT	<union1>	ALL	NULL	NULL	NULL	NULL	NULL	
+NULL	UNION RESULT	<union1,2>	ALL	NULL	NULL	NULL	NULL	NULL	
 explain select xx from t1 union select 1;
 ERROR 42S22: Unknown column 'xx' in 'field list'
 explain select a,b from t1 union select 1;
@@ -470,7 +470,7 @@ explain extended (select * from t1 where a=1) union (select * from t2 where a=1)
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	const	PRIMARY	PRIMARY	4	const	1	
 2	UNION	t2	const	PRIMARY	PRIMARY	4	const	1	
--1	UNION RESULT	<union1>	ALL	NULL	NULL	NULL	NULL	NULL	
+NULL	UNION RESULT	<union1,2>	ALL	NULL	NULL	NULL	NULL	NULL	
 Warnings:
 Note	1003	(select test.t1.a AS `a`,test.t1.b AS `b` from test.t1 where (test.t1.a = 1)) union (select test.t2.a AS `a`,test.t2.b AS `b` from test.t2 where (test.t2.a = 1))
 (select * from t1 where a=5) union (select * from t2 where a=1);
@@ -493,12 +493,12 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
 2	UNION	t1	index	PRIMARY	PRIMARY	4	NULL	4	Using index
 2	UNION	t2	index	PRIMARY	PRIMARY	4	NULL	3	Using where; Using index
--1	UNION RESULT	<union1>	ALL	NULL	NULL	NULL	NULL	NULL	
+NULL	UNION RESULT	<union1,2>	ALL	NULL	NULL	NULL	NULL	NULL	
 explain (select * from t1 where a=1) union (select * from t1 where b=1);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	const	PRIMARY	PRIMARY	4	const	1	
 2	UNION	t1	ref	b	b	5	const	1	Using where
--1	UNION RESULT	<union1>	ALL	NULL	NULL	NULL	NULL	NULL	
+NULL	UNION RESULT	<union1,2>	ALL	NULL	NULL	NULL	NULL	NULL	
 drop table t1,t2;
 create table t1 (   id int not null auto_increment, primary key (id)   ,user_name text );
 create table t2 (    id int not null auto_increment, primary key (id)   ,group_name text );

sql/sql_class.h

@@ -773,7 +773,7 @@ class THD :public ilink,
   uint	     current_tablenr,tmp_table;
   uint	     server_status,open_options,system_thread;
   uint32     db_length;
-  int        select_number;             //number of select (used for EXPLAIN)
+  uint       select_number;             //number of select (used for EXPLAIN)
   /* variables.transaction_isolation is reset to this after each commit */
   enum_tx_isolation session_tx_isolation;
   enum_check_fields count_cuted_fields;

sql/sql_lex.h

@@ -425,7 +425,7 @@ class st_select_lex: public st_select_lex_node
 
   ulong table_join_options;
   uint in_sum_expr;
-  int select_number; /* number of select (used for EXPLAIN) */
+  uint select_number; /* number of select (used for EXPLAIN) */
   uint with_wild; /* item list contain '*' */
   bool  braces;   	/* SELECT ... UNION (SELECT ... ) <- this braces */
   /* TRUE when having fix field called in processing of this SELECT */

sql/sql_select.cc

@@ -9133,7 +9133,7 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
 
   if (message)
   {
-    item_list.push_back(new Item_int((longlong)
+    item_list.push_back(new Item_int((int32)
 				     join->select_lex->select_number));
     item_list.push_back(new Item_string(join->select_lex->type,
 					strlen(join->select_lex->type), cs));
@@ -9146,23 +9146,44 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
   else if (join->select_lex == join->unit->fake_select_lex)
   {
     /* 
-       Here is guessing about fake_select_lex to avoid union SELECT
-       execution to get accurate information
+      here we assume that the query will return at least two rows, so we
+      show "filesort" in EXPLAIN. Of course, sometimes we'll be wrong
+      and no filesort will be actually done, but executing all selects in
+      the UNION to provide precise EXPLAIN information will hardly be
+      appreciated :)
     */
-    char table_name_buffer[64];
+    char table_name_buffer[NAME_LEN];
     item_list.empty();
     /* id */
-    item_list.push_back(new Item_int((int32)
-				     join->select_lex->select_number));
+    item_list.push_back(new Item_null);
     /* select_type */
     item_list.push_back(new Item_string(join->select_lex->type,
 					strlen(join->select_lex->type),
 					cs));
     /* table */
-    int len= my_snprintf(table_name_buffer, sizeof(table_name_buffer)-1,
-			 "<union%d>",
-			 -join->select_lex->select_number);
-    item_list.push_back(new Item_string(table_name_buffer, len, cs));
+    {
+      SELECT_LEX *sl= join->unit->first_select();
+      uint len= 6, lastop= 0;
+      memcpy(table_name_buffer, "<union", 6);
+      for (; sl && len + lastop + 5 < NAME_LEN; sl= sl->next_select())
+      {
+        len+= lastop;
+        lastop= my_snprintf(table_name_buffer + len, NAME_LEN - len,
+                            "%u,", sl->select_number);
+      }
+      if (sl || len + lastop >= NAME_LEN)
+      {
+        memcpy(table_name_buffer + len, "...>", 5);
+        len+= 4;
+      }
+      else
+      {
+        len+= lastop;
+        table_name_buffer[len - 1]= '>';  // change ',' to '>'
+      }
+      item_list.push_back(new Item_string(table_name_buffer, len, cs));
+    }
+    /* type */
     item_list.push_back(new Item_string(join_type_str[JT_ALL],
 					  strlen(join_type_str[JT_ALL]),
 					  cs));
@@ -9195,7 +9216,7 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
       TABLE *table=tab->table;
       char buff[512],*buff_ptr=buff;
       char buff1[512], buff2[512];
-      char table_name_buffer[64];
+      char table_name_buffer[NAME_LEN];
       String tmp1(buff1,sizeof(buff1),cs);
       String tmp2(buff2,sizeof(buff2),cs);
       tmp1.length(0);
@@ -9203,7 +9224,7 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
 
       item_list.empty();
       /* id */
-      item_list.push_back(new Item_int((int32)
+      item_list.push_back(new Item_uint((uint32)
 				       join->select_lex->select_number));
       /* select_type */
       item_list.push_back(new Item_string(join->select_lex->type,
@@ -9379,7 +9400,7 @@ int mysql_explain_union(THD *thd, SELECT_LEX_UNIT *unit, select_result *result)
   }
   if (first->next_select())
   {
-    unit->fake_select_lex->select_number= -first->select_number;
+    unit->fake_select_lex->select_number= UINT_MAX; // jost for initialization
     unit->fake_select_lex->type= "UNION RESULT";
     unit->fake_select_lex->options|= SELECT_DESCRIBE;
     if (!(res= unit->prepare(thd, result, SELECT_NO_UNLOCK | SELECT_DESCRIBE)))