Merge

2025-01-18 13:02:28 +01:00 · 2004-05-14 13:33:02 +03:00 · 2004-05-14 13:33:02 +03:00 · 71a374dc13
commit 71a374dc13
parent a71771788e 8885ce0dd7
11 changed files with 177 additions and 72 deletions
--- a/mysql-test/r/derived.result
+++ b/mysql-test/r/derived.result
@ -94,11 +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	
 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	
 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;
@ -246,8 +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	
 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	
 drop table t1;
 CREATE TABLE `t1` (
 `N` int(11) unsigned NOT NULL default '0',
--- a/mysql-test/r/subselect.result
+++ b/mysql-test/r/subselect.result
@ -16,6 +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	
 Warnings:
 Note	1249	Select 2 was reduced during optimisation
 Note	1249	Select 4 was reduced during optimisation
@ -28,6 +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	
 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))`
@ -182,6 +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	
 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;
@ -306,6 +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	
 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
@ -413,6 +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	
 Warnings:
 Note	1003	select 1 AS `1` from test.t1
 drop table t1;
@ -727,6 +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	
 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);
@ -1536,11 +1542,14 @@ e
 select * from t1 where 'f' > any (select s1 from t1 union select s1 from t1);
 s1
 e
-explain select * from t1 where 'f' > any (select s1 from t1 union select s1 from t1);
+explain extended select * from t1 where 'f' > any (select s1 from t1 union select s1 from t1);
 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	
+Warnings:
+Note	1003	select high_priority test.t1.s1 AS `s1` from test.t1
 drop table t1;
 CREATE TABLE t1 (number char(11) NOT NULL default '') ENGINE=MyISAM CHARSET=latin1;
 INSERT INTO t1 VALUES ('69294728265'),('18621828126'),('89356874041'),('95895001874');
--- a/mysql-test/r/union.result
+++ b/mysql-test/r/union.result
@ -86,6 +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
 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;
@ -106,21 +107,15 @@ 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	
 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;
-id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	4	
-2	UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+ERROR 21000: The used SELECT statements have a different number of columns
 explain select 1 union select a,b from t1 union select 1;
-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
-2	UNION	t1	ALL	NULL	NULL	NULL	NULL	4	
-3	UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+ERROR 21000: The used SELECT statements have a different number of columns
 explain select a,b from t1 union select 1 limit 0;
-id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
-2	UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+ERROR 21000: The used SELECT statements have a different number of columns
 select a,b from t1 into outfile 'skr' union select a,b from t2;
 ERROR HY000: Wrong usage of UNION and INTO
 select a,b from t1 order by a union select a,b from t2;
@ -475,6 +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	
 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);
@ -497,10 +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	
 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	
 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 );
@ -950,3 +948,8 @@ a
 1
 drop table t1, t2;
 set sql_select_limit=default;
+CREATE TABLE t1 (i int(11) default NULL,c char(1) default NULL,KEY i (i));
+CREATE TABLE t2 (i int(11) default NULL,c char(1) default NULL,KEY i (i));
+explain (select * from t1) union (select * from t2) order by not_existing_column;
+ERROR 42S22: Unknown column 'not_existing_column' in 'order clause'
+drop table t1, t2;
--- a/mysql-test/t/subselect.test
+++ b/mysql-test/t/subselect.test
@ -974,7 +974,7 @@ create table t1 (s1 char);
 insert into t1 values ('e');
 select * from t1 where 'f' > any (select s1 from t1);
 select * from t1 where 'f' > any (select s1 from t1 union select s1 from t1);
-explain select * from t1 where 'f' > any (select s1 from t1 union select s1 from t1);
+explain extended select * from t1 where 'f' > any (select s1 from t1 union select s1 from t1);
 drop table t1;

 #
--- a/mysql-test/t/union.test
+++ b/mysql-test/t/union.test
@ -39,8 +39,11 @@ explain select a,b from t1 union all select a,b from t2;

 --error  1054
 explain select xx from t1 union select 1;
+--error 1222
 explain select a,b from t1 union select 1;
+--error 1222
 explain select 1 union select a,b from t1 union select 1;
+--error 1222
 explain select a,b from t1 union select 1 limit 0;

 --error 1221
@ -515,3 +518,12 @@ SET SQL_SELECT_LIMIT=1;
 select a from t1 union select a from t2 order by a;
 drop table t1, t2;
 set sql_select_limit=default;
+
+#
+# nonexisting column in global ORDER BY
+#
+CREATE TABLE t1 (i int(11) default NULL,c char(1) default NULL,KEY i (i));
+CREATE TABLE t2 (i int(11) default NULL,c char(1) default NULL,KEY i (i));
+--error 1054
+explain (select * from t1) union (select * from t2) order by not_existing_column;
+drop table t1, t2;
--- a/sql/item.cc
+++ b/sql/item.cc
@ -369,9 +369,14 @@ const char *Item_ident::full_name() const
  }
  else
  {
-    tmp=(char*) sql_alloc((uint) strlen(table_name)+
-			  (uint) strlen(field_name)+2);
-    strxmov(tmp,table_name,".",field_name,NullS);
+    if (table_name[0])
+    {
+      tmp= (char*) sql_alloc((uint) strlen(table_name) +
+			     (uint) strlen(field_name) + 2);
+      strxmov(tmp, table_name, ".", field_name, NullS);
+    }
+    else
+      tmp= (char*) field_name;
  }
  return tmp;
 }
--- a/sql/sql_class.h
+++ b/sql/sql_class.h
@ -773,7 +773,7 @@ public:
  uint	     current_tablenr,tmp_table;
  uint	     server_status,open_options,system_thread;
  uint32     db_length;
-  uint       select_number;             //number of select (used for EXPLAIN)
+  int        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;
@ -1152,7 +1152,6 @@ class select_union :public select_result {
  TABLE *table;
  COPY_INFO info;
  TMP_TABLE_PARAM tmp_table_param;
-  bool not_describe;

  select_union(TABLE *table_par);
  ~select_union();
--- a/sql/sql_lex.cc
+++ b/sql/sql_lex.cc
@ -1007,6 +1007,7 @@ void st_select_lex_unit::init_query()
  fake_select_lex= 0;
  cleaned= 0;
  item_list.empty();
+  describe= 0;
 }

 void st_select_lex::init_query()
--- a/sql/sql_lex.h
+++ b/sql/sql_lex.h
@ -339,6 +339,7 @@ public:
  st_select_lex *fake_select_lex;

  st_select_lex *union_distinct; /* pointer to the last UNION DISTINCT */
+  bool describe; /* union exec() called for EXPLAIN */

  void init_query();
  bool create_total_list(THD *thd, st_lex *lex, TABLE_LIST **result);
@ -423,7 +424,7 @@ public:

  ulong table_join_options;
  uint in_sum_expr;
-  uint select_number; /* number of select (used for EXPLAIN) */
+  int 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 */
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@ -9134,7 +9134,8 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,

  if (message)
  {
-    item_list.push_back(new Item_int((int32) join->select_lex->select_number));
+    item_list.push_back(new Item_int((longlong)
+				     join->select_lex->select_number));
    item_list.push_back(new Item_string(join->select_lex->type,
 					strlen(join->select_lex->type), cs));
    for (uint i=0 ; i < 7; i++)
@ -9143,6 +9144,49 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
    if (result->send_data(item_list))
      join->error= 1;
  }
+  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
+    */
+    char table_name_buffer[64];
+    item_list.empty();
+    /* id */
+    item_list.push_back(new Item_int((int32)
+				     join->select_lex->select_number));
+    /* 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));
+    item_list.push_back(new Item_string(join_type_str[JT_ALL],
+					  strlen(join_type_str[JT_ALL]),
+					  cs));
+    /* possible_keys */
+    item_list.push_back(item_null);
+    /* key*/
+    item_list.push_back(item_null);
+    /* key_len */
+    item_list.push_back(item_null);
+    /* ref */
+    item_list.push_back(item_null);
+    /* rows */
+    item_list.push_back(item_null);
+    /* extra */
+    if (join->unit->global_parameters->order_list.first)
+      item_list.push_back(new Item_string("Using filesort",
+					  14, cs));
+    else
+      item_list.push_back(new Item_string("", 0, cs));
+
+    if (result->send_data(item_list))
+      join->error= 1;
+  }
  else
  {
    table_map used_tables=0;
@ -9152,36 +9196,41 @@ 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 derived_name[64];
+      char table_name_buffer[64];
      String tmp1(buff1,sizeof(buff1),cs);
      String tmp2(buff2,sizeof(buff2),cs);
      tmp1.length(0);
      tmp2.length(0);

      item_list.empty();
+      /* id */
      item_list.push_back(new Item_int((int32)
 				       join->select_lex->select_number));
+      /* select_type */
      item_list.push_back(new Item_string(join->select_lex->type,
 					  strlen(join->select_lex->type),
 					  cs));
      if (tab->type == JT_ALL && tab->select && tab->select->quick)
 	tab->type= JT_RANGE;
+      /* table */
      if (table->derived_select_number)
      {
 	/* Derived table name generation */
-	int len= my_snprintf(derived_name, sizeof(derived_name)-1,
+	int len= my_snprintf(table_name_buffer, sizeof(table_name_buffer)-1,
 			     "<derived%u>",
 			     table->derived_select_number);
-	item_list.push_back(new Item_string(derived_name, len, cs));
+	item_list.push_back(new Item_string(table_name_buffer, len, cs));
      }
      else
 	item_list.push_back(new Item_string(table->table_name,
 					    strlen(table->table_name),
 					    cs));
+      /* type */
      item_list.push_back(new Item_string(join_type_str[tab->type],
 					  strlen(join_type_str[tab->type]),
 					  cs));
      uint j;
+      /* possible_keys */
      if (!tab->keys.is_clear_all())
      {
        for (j=0 ; j < table->keys ; j++)
@ -9198,6 +9247,7 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
 	item_list.push_back(new Item_string(tmp1.ptr(),tmp1.length(),cs));
      else
 	item_list.push_back(item_null);
+      /* key key_len ref */
      if (tab->ref.key_parts)
      {
 	KEY *key_info=table->key_info+ tab->ref.key;
@ -9236,9 +9286,11 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
 	item_list.push_back(item_null);
 	item_list.push_back(item_null);
      }
+      /* rows */
      item_list.push_back(new Item_int((longlong) (ulonglong)
 				       join->best_positions[i]. records_read,
 				       21));
+      /* extra */
      my_bool key_read=table->key_read;
      if ((tab->type == JT_NEXT || tab->type == JT_CONST) &&
          table->used_keys.is_set(tab->index))
@ -9303,32 +9355,53 @@ int mysql_explain_union(THD *thd, SELECT_LEX_UNIT *unit, select_result *result)
  DBUG_ENTER("mysql_explain_union");
  int res= 0;
  SELECT_LEX *first= unit->first_select();
+
  for (SELECT_LEX *sl= first;
       sl;
       sl= sl->next_select())
  {
    // drop UNCACHEABLE_EXPLAIN, because it is for internal usage only
    uint8 uncacheable= (sl->uncacheable & ~UNCACHEABLE_EXPLAIN);
-
-    res= mysql_explain_select(thd, sl,
-			      (((&thd->lex->select_lex)==sl)?
-			       ((thd->lex->all_selects_list != sl) ? 
-				primary_key_name : "SIMPLE"):
-			       ((sl == first)?
-				((sl->linkage == DERIVED_TABLE_TYPE) ?
-				 "DERIVED":
-				((uncacheable & UNCACHEABLE_DEPENDENT) ?
-				 "DEPENDENT SUBQUERY":
-				 (uncacheable?"UNCACHEABLE SUBQUERY":
-				   "SUBQUERY"))):
-				((uncacheable & UNCACHEABLE_DEPENDENT) ?
-				 "DEPENDENT UNION":
-				 uncacheable?"UNCACHEABLE UNION":
-				  "UNION"))),
-			      result);
-    if (res)
-      break;
-
+    sl->type= (((&thd->lex->select_lex)==sl)?
+	       ((thd->lex->all_selects_list != sl) ? 
+		primary_key_name : "SIMPLE"):
+	       ((sl == first)?
+		((sl->linkage == DERIVED_TABLE_TYPE) ?
+		 "DERIVED":
+		 ((uncacheable & UNCACHEABLE_DEPENDENT) ?
+		  "DEPENDENT SUBQUERY":
+		  (uncacheable?"UNCACHEABLE SUBQUERY":
+		   "SUBQUERY"))):
+		((uncacheable & UNCACHEABLE_DEPENDENT) ?
+		 "DEPENDENT UNION":
+		 uncacheable?"UNCACHEABLE UNION":
+		 "UNION")));
+    sl->options|= SELECT_DESCRIBE;
+  }
+  if (first->next_select())
+  {
+    unit->fake_select_lex->select_number= -first->select_number;
+    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)))
+      res= unit->exec();
+    res|= unit->cleanup();
+  }
+  else
+  {
+    thd->lex->current_select= first;
+    res= mysql_select(thd, &first->ref_pointer_array,
+			(TABLE_LIST*) first->table_list.first,
+			first->with_wild, first->item_list,
+			first->where,
+			first->order_list.elements +
+			first->group_list.elements,
+			(ORDER*) first->order_list.first,
+			(ORDER*) first->group_list.first,
+			first->having,
+			(ORDER*) thd->lex->proc_list.first,
+			first->options | thd->options | SELECT_DESCRIBE,
+			result, unit, first);
  }
  if (res > 0 || thd->net.report_error)
    res= -1; // mysql_explain_select do not report error
@ -9336,30 +9409,6 @@ int mysql_explain_union(THD *thd, SELECT_LEX_UNIT *unit, select_result *result)
 }


-int mysql_explain_select(THD *thd, SELECT_LEX *select_lex, char const *type, 
-			 select_result *result)
-{
-  DBUG_ENTER("mysql_explain_select");
-  DBUG_PRINT("info", ("Select 0x%lx, type %s", (ulong)select_lex, type))
-  select_lex->type= type;
-  thd->lex->current_select= select_lex;
-  SELECT_LEX_UNIT *unit=  select_lex->master_unit();
-  int res= mysql_select(thd, &select_lex->ref_pointer_array,
-			(TABLE_LIST*) select_lex->table_list.first,
-			select_lex->with_wild, select_lex->item_list,
-			select_lex->where,
-			select_lex->order_list.elements +
-			select_lex->group_list.elements,
-			(ORDER*) select_lex->order_list.first,
-			(ORDER*) select_lex->group_list.first,
-			select_lex->having,
-			(ORDER*) thd->lex->proc_list.first,
-			select_lex->options | thd->options | SELECT_DESCRIBE,
-			result, unit, select_lex);
-  DBUG_RETURN(res);
-}
-
-
 void st_select_lex::print(THD *thd, String *str)
 {
  if (!thd)
--- a/sql/sql_union.cc
+++ b/sql/sql_union.cc
@ -41,7 +41,7 @@ int mysql_union(THD *thd, LEX *lex, select_result *result,
 ***************************************************************************/

 select_union::select_union(TABLE *table_par)
-  :table(table_par), not_describe(0)
+  :table(table_par)
 {
  bzero((char*) &info,sizeof(info));
  /*
@ -149,6 +149,8 @@ int st_select_lex_unit::prepare(THD *thd_arg, select_result *sel_result,
  select_result *tmp_result;
  DBUG_ENTER("st_select_lex_unit::prepare");

+  describe= test(additional_options & SELECT_DESCRIBE);
+
  /*
    result object should be reassigned even if preparing already done for
    max/min subquery (ALL/ANY optimization)
@ -156,7 +158,26 @@ int st_select_lex_unit::prepare(THD *thd_arg, select_result *sel_result,
  result= sel_result;

  if (prepared)
+  {
+    if (describe)
+    {
+      /* fast reinit for EXPLAIN */
+      for (sl= first_select_in_union(); sl; sl= sl->next_select())
+      {
+	sl->join->result= result;
+	select_limit_cnt= HA_POS_ERROR;
+	offset_limit_cnt= 0;
+	if (!sl->join->procedure &&
+	    result->prepare(sl->join->fields_list, this))
+	{
+	  DBUG_RETURN(1);
+	}
+	sl->join->select_options|= SELECT_DESCRIBE;
+	sl->join->reinit();
+      }
+    }
    DBUG_RETURN(0);
+  }
  prepared= 1;
  res= 0;
  
@ -169,8 +190,9 @@ int st_select_lex_unit::prepare(THD *thd_arg, select_result *sel_result,
  {
    if (!(tmp_result= union_result= new select_union(0)))
      goto err;
-    union_result->not_describe= 1;
    union_result->tmp_table_param.init();
+    if (describe)
+      tmp_result= sel_result;
  }
  else
  {
@ -327,11 +349,11 @@ int st_select_lex_unit::exec()
  ulonglong add_rows=0;
  DBUG_ENTER("st_select_lex_unit::exec");

-  if (executed && !uncacheable)
+  if (executed && !uncacheable && !describe)
    DBUG_RETURN(0);
  executed= 1;
  
-  if (uncacheable || !item || !item->assigned())
+  if (uncacheable || !item || !item->assigned() || describe)
  {
    if (optimized && item && item->assigned())
    {
@ -350,7 +372,7 @@ int st_select_lex_unit::exec()
 	res= sl->join->reinit();
      else
      {
-	if (sl != global_parameters)
+	if (sl != global_parameters && !describe)
 	{
 	  offset_limit_cnt= sl->offset_limit;
 	  select_limit_cnt= sl->select_limit+sl->offset_limit;
@ -362,7 +384,7 @@ int st_select_lex_unit::exec()
 	    We can't use LIMIT at this stage if we are using ORDER BY for the
 	    whole query
 	  */
-	  if (sl->order_list.first)
+	  if (sl->order_list.first || describe)
 	    select_limit_cnt= HA_POS_ERROR;
 	  else
 	    select_limit_cnt= sl->select_limit+sl->offset_limit;