Added index_merge access method

BitKeeper/etc/logging_ok

@@ -95,6 +95,7 @@ peter@linux.local
 peter@mysql.com
 peterg@mysql.com
 pgulutzan@linux.local
+psergey@psergey.(none)
 ram@gw.udmsearch.izhnet.ru
 ram@mysql.r18.ru
 ram@ram.(none)

sql/opt_ft.cc

@@ -26,7 +26,7 @@
 ** Create a FT or QUICK RANGE based on a key
 ****************************************************************************/
 
-QUICK_SELECT *get_ft_or_quick_select_for_ref(TABLE *table, JOIN_TAB *tab)
+QUICK_RANGE_SELECT *get_ft_or_quick_select_for_ref(TABLE *table, JOIN_TAB *tab)
 {
   if (tab->type == JT_FT)
     return new FT_SELECT(table, &tab->ref);

sql/opt_ft.h

@@ -24,17 +24,18 @@
 #pragma interface			/* gcc class implementation */
 #endif
 
-class FT_SELECT: public QUICK_SELECT {
+class FT_SELECT: public QUICK_RANGE_SELECT {
 public:
   TABLE_REF *ref;
 
   FT_SELECT(TABLE *table, TABLE_REF *tref) :
-      QUICK_SELECT (table,tref->key,1), ref(tref) { init(); }
+      QUICK_RANGE_SELECT (table,tref->key,1), ref(tref) { init(); }
   
-  int init() { return error=file->ft_init(); }
+  int init() { QUICK_RANGE_SELECT::init(); return (error=file->ft_init()); }
   int get_next() { return error=file->ft_read(record); }
+  int get_type() { return QS_TYPE_FULLTEXT; }
 };
 
-QUICK_SELECT *get_ft_or_quick_select_for_ref(TABLE *table, JOIN_TAB *tab);
+QUICK_RANGE_SELECT *get_ft_or_quick_select_for_ref(TABLE *table, JOIN_TAB *tab);
 
 #endif

sql/opt_range.h

@@ -65,41 +65,198 @@ class QUICK_RANGE :public Sql_alloc {
     }
 };
 
+class INDEX_MERGE; 
 
-class QUICK_SELECT {
+/*
+  Quick select interface. 
+  This class is parent for all QUICK_*_SELECT and FT_SELECT classes.
+*/
+
+class QUICK_SELECT_I
+{
 public:
+  ha_rows records;  /* estimate of # of records to be retrieved */
+  double  read_time; /* time to perform this retrieval          */
+  TABLE   *head;
+
+  /*
+    the only index this quick select uses, or MAX_KEY for 
+    QUICK_INDEX_MERGE_SELECT
+  */
+  uint index; 
+  uint max_used_key_length, used_key_parts;
+
+  QUICK_SELECT_I();
+  virtual ~QUICK_SELECT_I(){};
+  virtual int  init() = 0;
+  virtual void reset(void) = 0;
+  virtual int  get_next() = 0;   /* get next record to retrieve */
+  virtual bool reverse_sorted() = 0;
+  virtual bool unique_key_range() { return false; }
+
+  enum { 
+    QS_TYPE_RANGE = 0,
+    QS_TYPE_INDEX_MERGE = 1,
+    QS_TYPE_RANGE_DESC = 2,
+    QS_TYPE_FULLTEXT   = 3
+  };
+
+  /* Get type of this quick select - one of the QS_* values */
+  virtual int get_type() = 0; 
+};
+
+struct st_qsel_param;
+class SEL_ARG;
+
+class QUICK_RANGE_SELECT : public QUICK_SELECT_I 
+{
+protected:
   bool next,dont_free;
+public:
   int error;
-  uint index, max_used_key_length, used_key_parts;
-  TABLE *head;
   handler *file;
   byte    *record;
+protected:
+  friend void print_quick_sel_range(QUICK_RANGE_SELECT *quick,
+                                    key_map needed_reg);
+  friend QUICK_RANGE_SELECT *get_quick_select_for_ref(TABLE *table, 
+                                                      struct st_table_ref *ref);
+  friend bool get_quick_keys(struct st_qsel_param *param,
+                             QUICK_RANGE_SELECT *quick,KEY_PART *key,
+                             SEL_ARG *key_tree,char *min_key,uint min_key_flag,
+                             char *max_key, uint max_key_flag);
+  friend QUICK_RANGE_SELECT *get_quick_select(struct st_qsel_param*,uint idx,
+                                              SEL_ARG *key_tree,
+                                              MEM_ROOT *alloc);
+  friend class QUICK_SELECT_DESC;
+
   List<QUICK_RANGE> ranges;
   List_iterator<QUICK_RANGE> it;
   QUICK_RANGE *range;
   MEM_ROOT alloc;
-
   KEY_PART *key_parts;
-  ha_rows records;
-  double read_time;
+  int cmp_next(QUICK_RANGE *range);
+public:
+  QUICK_RANGE_SELECT(TABLE *table,uint index_arg,bool no_alloc=0, 
+                     MEM_ROOT *parent_alloc=NULL);
+  ~QUICK_RANGE_SELECT();
   
-  QUICK_SELECT(TABLE *table,uint index_arg,bool no_alloc=0);
-  virtual ~QUICK_SELECT();
   void reset(void) { next=0; it.rewind(); }
-  int init() { return error=file->index_init(index); }
-  virtual int get_next();
-  virtual bool reverse_sorted() { return 0; }
-  int cmp_next(QUICK_RANGE *range);
+  int init();
+  int get_next();
+  bool reverse_sorted() { return 0; }
   bool unique_key_range();
+  int get_type() { return QS_TYPE_RANGE; }
 };
 
+/*
+  Helper class for keeping track of rows that have been passed to output 
+  in index_merge access method. 
+
+  NOTES
+    Current implementation uses a temporary table to store ROWIDs of rows that
+    have been passed to output. In the future it might be changed to use more 
+    efficient mechanisms, like Unique class.
+*/
+
+class INDEX_MERGE
+{
+public:
+  INDEX_MERGE(THD *thd_arg);
+  ~INDEX_MERGE(); 
+  
+  int init(TABLE *table);
+  int check_record_in();
+  int start_last_quick_select();
+  int error;
+private:
+  /* The only field in temporary table */
+  class Item_rowid : public Item_str_func
+  {
+    TABLE *head; /* source table */
+  public:
+    Item_rowid(TABLE *table) : head(table) 
+    {
+      max_length= table->file->ref_length;
+      collation.set(&my_charset_bin);
+    };
+    const char *func_name() const { return "rowid"; }
+    bool const_item() const { return 0; }
+    String *val_str(String *);
+    void fix_length_and_dec()
+    {}
+  };
+
+  /* Check if record has been processed and save it if it wasn't  */
+  inline int put_record(); 
+  
+  /* Check if record has been processed without saving it         */
+  inline int check_record();
+  
+  /* If true, check_record_in does't store ROWIDs it is passed.   */
+  bool  dont_save;
+
+  THD *thd;
+  TABLE *head;                     /* source table                        */
+  TABLE *temp_table;               /* temp. table used for values storage */
+  TMP_TABLE_PARAM tmp_table_param; /* temp. table creation parameters     */
+  Item_rowid *rowid_item;          /* the only field in temp. table       */
+  List<Item> fields;               /* temp. table fields list 
+                                      (the only element is rowid_item)    */
+  ORDER order;                     /* key for temp. table (rowid_item)    */
+};
+
+
+/*
+  Index merge quick select. 
+  It is implemented as a container for several QUICK_RANGE_SELECTs.
+*/
+
+class QUICK_INDEX_MERGE_SELECT : public QUICK_SELECT_I 
+{
+public:
+  QUICK_INDEX_MERGE_SELECT(THD *thd, TABLE *table);
+  ~QUICK_INDEX_MERGE_SELECT();
+
+  int  init();
+  void reset(void);
+  int  get_next();
+  bool reverse_sorted() { return false; }
+  bool unique_key_range() { return false; }
+  int get_type() { return QS_TYPE_INDEX_MERGE; }
+
+  bool push_quick_back(QUICK_RANGE_SELECT *quick_sel_range);
+
+  /* range quick selects this index_merge read consists of */
+  List<QUICK_RANGE_SELECT> quick_selects;
+  
+  /* quick select which is currently used for rows retrieval */
+  List_iterator_fast<QUICK_RANGE_SELECT> cur_quick_it;
+  QUICK_RANGE_SELECT* cur_quick_select;
+  
+  /*
+    Last element in quick_selects list. 
+    INDEX_MERGE::start_last_quick_select is called before retrieving
+    rows for it. 
+  */
+  QUICK_RANGE_SELECT* last_quick_select;
+  
+  /*
+    Used to keep track of what records have been already passed to output 
+    when doing index_merge access (NULL means no index_merge) 
+  */
+  INDEX_MERGE index_merge;
+
+  MEM_ROOT    alloc;
+};
 
-class QUICK_SELECT_DESC: public QUICK_SELECT
+class QUICK_SELECT_DESC: public QUICK_RANGE_SELECT
 {
 public:
-  QUICK_SELECT_DESC(QUICK_SELECT *q, uint used_key_parts);
+  QUICK_SELECT_DESC(QUICK_RANGE_SELECT *q, uint used_key_parts);
   int get_next();
   bool reverse_sorted() { return 1; }
+  int get_type() { return QS_TYPE_RANGE_DESC; }
 private:
   int cmp_prev(QUICK_RANGE *range);
   bool range_reads_after_key(QUICK_RANGE *range);
@@ -114,7 +271,7 @@ private:
 
 class SQL_SELECT :public Sql_alloc {
  public:
-  QUICK_SELECT *quick;		// If quick-select used
+  QUICK_SELECT_I *quick;	// If quick-select used
   COND		*cond;		// where condition
   TABLE	*head;
   IO_CACHE file;		// Positions to used records
@@ -134,6 +291,6 @@ class SQL_SELECT :public Sql_alloc {
 			bool force_quick_range=0);
 };
 
-QUICK_SELECT *get_quick_select_for_ref(TABLE *table, struct st_table_ref *ref);
+QUICK_RANGE_SELECT *get_quick_select_for_ref(TABLE *table, struct st_table_ref *ref);
 
 #endif

sql/sql_class.cc

@@ -537,8 +537,8 @@ int THD::send_explain_fields(select_result *result)
   item->maybe_null=1;
   field_list.push_back(item=new Item_empty_string("key",NAME_LEN));
   item->maybe_null=1;
-  field_list.push_back(item=new Item_return_int("key_len",3,
-						MYSQL_TYPE_LONGLONG));
+  field_list.push_back(item=new Item_empty_string("key_len",
+						  NAME_LEN*MAX_KEY));
   item->maybe_null=1;
   field_list.push_back(item=new Item_empty_string("ref",
 						  NAME_LEN*MAX_REF_PARTS));

sql/sql_list.h

@@ -135,6 +135,12 @@ public:
       last= &first;
     return tmp->info;
   }
+  inline void concat(base_list *list)
+  {
+    *last= list->first;
+    last= list->last;
+    elements+= list->elements;
+  }
   inline list_node* last_node() { return *last; }
   inline list_node* first_node() { return first;}
   inline void *head() { return first->info; }
@@ -255,6 +261,7 @@ public:
     }
     empty();
   }
+  inline void concat(List<T> *list) { base_list::concat(list); }
 };
 
 

sql/sql_select.cc

@@ -32,7 +32,8 @@
 
 const char *join_type_str[]={ "UNKNOWN","system","const","eq_ref","ref",
 			      "MAYBE_REF","ALL","range","index","fulltext",
-			      "ref_or_null","simple_in","index_in"
+			      "ref_or_null","simple_in","index_in",
+                              "index_merge"
 };
 
 static void optimize_keyuse(JOIN *join, DYNAMIC_ARRAY *keyuse_array);
@@ -114,7 +115,6 @@ static int join_read_next_same_or_null(READ_RECORD *info);
 static COND *make_cond_for_table(COND *cond,table_map table,
 				 table_map used_table);
 static Item* part_of_refkey(TABLE *form,Field *field);
-static uint find_shortest_key(TABLE *table, key_map usable_keys);
 static bool test_if_skip_sort_order(JOIN_TAB *tab,ORDER *order,
 				    ha_rows select_limit, bool no_changes);
 static int create_sort_index(THD *thd, JOIN *join, ORDER *order,
@@ -6473,7 +6473,7 @@ static int test_if_order_by_key(ORDER *order, TABLE *table, uint idx,
   return reverse;
 }
 
-static uint find_shortest_key(TABLE *table, key_map usable_keys)
+uint find_shortest_key(TABLE *table, key_map usable_keys)
 {
   uint min_length= (uint) ~0;
   uint best= MAX_KEY;
@@ -6601,6 +6601,9 @@ test_if_skip_sort_order(JOIN_TAB *tab,ORDER *order,ha_rows select_limit,
   }
   else if (select && select->quick)		// Range found by opt_range
   {
+    /* assume results are not ordered when index merge is used */
+    if (select->quick->get_type() == QUICK_SELECT_I::QS_TYPE_INDEX_MERGE)
+      DBUG_RETURN(0);
     ref_key=	   select->quick->index;
     ref_key_parts= select->quick->used_key_parts;
   }
@@ -6635,6 +6638,10 @@ test_if_skip_sort_order(JOIN_TAB *tab,ORDER *order,ha_rows select_limit,
 	}
 	else
 	{
+          /* 
+            We have verified above that select->quick is not 
+            index_merge quick select. 
+          */
 	  select->quick->index= new_ref_key;
 	  select->quick->init();
 	}
@@ -6656,10 +6663,13 @@ test_if_skip_sort_order(JOIN_TAB *tab,ORDER *order,ha_rows select_limit,
 	  */
 	  if (!select->quick->reverse_sorted())
 	  {
-            if (table->file->index_flags(ref_key) & HA_NOT_READ_PREFIX_LAST)
+            if (table->file->index_flags(ref_key) & HA_NOT_READ_PREFIX_LAST ||
+                (select->quick->get_type() == 
+                QUICK_SELECT_I::QS_TYPE_INDEX_MERGE))
               DBUG_RETURN(0);			// Use filesort
+            
             // ORDER BY range_key DESC
-	    QUICK_SELECT_DESC *tmp=new QUICK_SELECT_DESC(select->quick,
+	    QUICK_SELECT_DESC *tmp=new QUICK_SELECT_DESC((QUICK_RANGE_SELECT*)(select->quick),
 							 used_key_parts);
 	    if (!tmp || tmp->error)
 	    {
@@ -6794,8 +6804,11 @@ create_sort_index(THD *thd, JOIN *join, ORDER *order,
     {
       select->quick=tab->quick;
       tab->quick=0;
-      /* We can only use 'Only index' if quick key is same as ref_key */
-      if (table->key_read && (uint) tab->ref.key != select->quick->index)
+      /* 
+        We can only use 'Only index' if quick key is same as ref_key
+        and in index_merge 'Only index' cannot be used
+      */
+      if (table->key_read && ((uint) tab->ref.key != select->quick->index))
       {
 	table->key_read=0;
 	table->file->extra(HA_EXTRA_NO_KEYREAD);
@@ -8598,12 +8611,15 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
       JOIN_TAB *tab=join->join_tab+i;
       TABLE *table=tab->table;
       char buff[512],*buff_ptr=buff;
-      char buff1[512], buff2[512];
+      char buff1[512], buff2[512], buff3[512];
+      char keylen_str_buf[64];
       char derived_name[64];
       String tmp1(buff1,sizeof(buff1),cs);
       String tmp2(buff2,sizeof(buff2),cs);
+      String tmp3(buff3,sizeof(buff3),cs);
       tmp1.length(0);
       tmp2.length(0);
+      tmp3.length(0);
 
       item_list.empty();
       item_list.push_back(new Item_int((int32) 
@@ -8612,7 +8628,13 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
 					  strlen(join->select_lex->type),
 					  cs));
       if (tab->type == JT_ALL && tab->select && tab->select->quick)
-	tab->type= JT_RANGE;
+      {
+        if (tab->select->quick->get_type() == 
+            QUICK_SELECT_I::QS_TYPE_INDEX_MERGE)
+          tab->type = JT_INDEX_MERGE;
+        else
+	  tab->type = JT_RANGE;
+      }
       if (table->derived_select_number)
       {
 	/* Derived table name generation */
@@ -8646,10 +8668,14 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
       if (tab->ref.key_parts)
       {
 	KEY *key_info=table->key_info+ tab->ref.key;
+        register uint length;
 	item_list.push_back(new Item_string(key_info->name,
 					    strlen(key_info->name),
 					    system_charset_info));
-	item_list.push_back(new Item_int((int32) tab->ref.key_length));
+        length= longlong2str(tab->ref.key_length, keylen_str_buf, 10) - 
+                keylen_str_buf;
+        item_list.push_back(new Item_string(keylen_str_buf, length,
+                                            system_charset_info));
 	for (store_key **ref=tab->ref.key_copy ; *ref ; ref++)
 	{
 	  if (tmp2.length())
@@ -8661,18 +8687,60 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
       else if (tab->type == JT_NEXT)
       {
 	KEY *key_info=table->key_info+ tab->index;
+        register uint length;
 	item_list.push_back(new Item_string(key_info->name,
 					    strlen(key_info->name),cs));
-	item_list.push_back(new Item_int((int32) key_info->key_length));
+        length= longlong2str(key_info->key_length, keylen_str_buf, 10) - 
+                keylen_str_buf;
+        item_list.push_back(new Item_string(keylen_str_buf, 
+                                            length,
+                                            system_charset_info));
 	item_list.push_back(item_null);
       }
       else if (tab->select && tab->select->quick)
       {
-	KEY *key_info=table->key_info+ tab->select->quick->index;
-	item_list.push_back(new Item_string(key_info->name,
-					    strlen(key_info->name),cs));
-	item_list.push_back(new Item_int((int32) tab->select->quick->
-					 max_used_key_length));
+        if (tab->select->quick->get_type() == 
+            QUICK_SELECT_I::QS_TYPE_INDEX_MERGE)
+        {
+          QUICK_INDEX_MERGE_SELECT *quick_imerge=
+            (QUICK_INDEX_MERGE_SELECT*)tab->select->quick;
+          QUICK_RANGE_SELECT *quick;
+
+          List_iterator_fast<QUICK_RANGE_SELECT> it(quick_imerge->
+                                                    quick_selects);
+          while ((quick= it++))
+          {
+	    KEY *key_info= table->key_info + quick->index;
+            register uint length;
+            if (tmp3.length())
+	      tmp3.append(',');
+	    
+            tmp3.append(key_info->name);
+
+	    if (tmp2.length())
+	      tmp2.append(',');
+
+            length= longlong2str(quick->max_used_key_length, keylen_str_buf,
+                                 10) - 
+                    keylen_str_buf;
+
+            tmp2.append(keylen_str_buf, length);
+          }
+        }
+        else
+        {
+	  KEY *key_info= table->key_info + tab->select->quick->index;
+          register uint length;
+          tmp3.append(key_info->name);
+          
+          length= longlong2str(tab->select->quick->max_used_key_length, 
+                               keylen_str_buf, 10) -
+                  keylen_str_buf;
+          tmp2.append(keylen_str_buf, length);
+        }
+
+	item_list.push_back(new Item_string(tmp3.ptr(),tmp3.length(),cs));
+	item_list.push_back(new Item_string(tmp2.ptr(),tmp2.length(),cs));
 	item_list.push_back(item_null);
       }
       else

sql/sql_select.h

@@ -76,7 +76,7 @@ typedef struct st_join_cache {
 
 enum join_type { JT_UNKNOWN,JT_SYSTEM,JT_CONST,JT_EQ_REF,JT_REF,JT_MAYBE_REF,
 		 JT_ALL, JT_RANGE, JT_NEXT, JT_FT, JT_REF_OR_NULL,
-		 JT_SIMPLE_IN, JT_INDEX_IN};
+		 JT_SIMPLE_IN, JT_INDEX_IN, JT_INDEX_MERGE}; 
 
 class JOIN;
 
@@ -85,7 +85,7 @@ typedef struct st_join_table {
   KEYUSE	*keyuse;			/* pointer to first used key */
   SQL_SELECT	*select;
   COND		*select_cond;
-  QUICK_SELECT	*quick;
+  QUICK_SELECT_I *quick;
   Item		*on_expr;
   const char	*info;
   byte		*null_ref_key;
@@ -307,6 +307,7 @@ void copy_fields(TMP_TABLE_PARAM *param);
 void copy_funcs(Item **func_ptr);
 bool create_myisam_from_heap(THD *thd, TABLE *table, TMP_TABLE_PARAM *param,
 			     int error, bool ignore_last_dupp_error);
+uint find_shortest_key(TABLE *table, key_map usable_keys);
 
 /* functions from opt_sum.cc */
 int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds);

sql/sql_test.cc

@@ -179,9 +179,39 @@ TEST_join(JOIN *join)
 		"                  quick select checked for each record (keys: %d)\n",
 		(int) tab->select->quick_keys);
       else if (tab->select->quick)
-	fprintf(DBUG_FILE,"                  quick select used on key %s, length: %d\n",
+      {
+        int quick_type= tab->select->quick->get_type();
+        if ((quick_type == QUICK_SELECT_I::QS_TYPE_RANGE) || 
+            (quick_type == QUICK_SELECT_I::QS_TYPE_RANGE_DESC))
+        {
+	  fprintf(DBUG_FILE,
+                "                  quick select used on key %s, length: %d\n",
 		form->key_info[tab->select->quick->index].name,
 		tab->select->quick->max_used_key_length);
+        }
+        else if (quick_type == QUICK_SELECT_I::QS_TYPE_INDEX_MERGE)
+        {
+          QUICK_INDEX_MERGE_SELECT *quick_imerge= 
+              (QUICK_INDEX_MERGE_SELECT*)tab->select->quick;
+          QUICK_RANGE_SELECT *quick;
+          fprintf(DBUG_FILE,
+                  "                  index_merge quick select used\n");
+                    
+          List_iterator_fast<QUICK_RANGE_SELECT> it(quick_imerge->quick_selects);
+          while ((quick = it++))
+          {
+  	    fprintf(DBUG_FILE,
+                "                  range quick select: key %s, length: %d\n",
+		form->key_info[quick->index].name,
+		quick->max_used_key_length);
+          }
+        }
+        else
+        {
+          fprintf(DBUG_FILE,
+                  "                  quick select of unknown nature used\n");
+        }
+      }
       else
 	VOID(fputs("                  select used\n",DBUG_FILE));
     }

sql/sql_union.cc

@@ -117,6 +117,7 @@ int st_select_lex_unit::prepare(THD *thd, select_result *sel_result,
 {
   SELECT_LEX *lex_select_save= thd->lex.current_select;
   SELECT_LEX *select_cursor;
+  SELECT_LEX *sl;
   DBUG_ENTER("st_select_lex_unit::prepare");  
 
   if (prepared)
@@ -185,7 +186,7 @@ int st_select_lex_unit::prepare(THD *thd, select_result *sel_result,
   union_result->not_describe=1;
   union_result->tmp_table_param=tmp_table_param;
 
-  for (SELECT_LEX *sl= select_cursor; sl; sl= sl->next_select())
+  for (sl= select_cursor; sl; sl= sl->next_select())
   {
     JOIN *join= new JOIN(thd, sl->item_list, 
 			 sl->options | thd->options | SELECT_NO_UNLOCK,

sql/sql_update.cc

@@ -171,10 +171,18 @@ int mysql_update(THD *thd,
   init_ftfuncs(thd, &thd->lex.select_lex, 1);
   /* Check if we are modifying a key that we are used to search with */
   if (select && select->quick)
+  {
+    if (select->quick->get_type() != QUICK_SELECT_I::QS_TYPE_INDEX_MERGE)
+    {
+      used_index= select->quick->index;
       used_key_is_modified= (!select->quick->unique_key_range() &&
-			   check_if_key_used(table,
-					     (used_index=select->quick->index),
-					     fields));
+			      check_if_key_used(table,used_index,fields));
+    }
+    else
+    {
+      used_key_is_modified= true;
+    }
+  }
   else if ((used_index=table->file->key_used_on_scan) < MAX_KEY)
     used_key_is_modified=check_if_key_used(table, used_index, fields);
   else
@@ -688,8 +696,26 @@ static bool safe_update_on_fly(JOIN_TAB *join_tab, List<Item> *fields)
   case JT_ALL:
     /* If range search on index */
     if (join_tab->quick)
-      return !check_if_key_used(table, join_tab->quick->index,
-				*fields);
+    {
+      if (join_tab->quick->get_type() != QUICK_SELECT_I::QS_TYPE_INDEX_MERGE)
+      {
+        return !check_if_key_used(table,join_tab->quick->index,*fields);
+      }
+      else
+      {
+        QUICK_INDEX_MERGE_SELECT *qsel_imerge=
+          (QUICK_INDEX_MERGE_SELECT*)(join_tab->quick);
+        List_iterator_fast<QUICK_RANGE_SELECT> it(qsel_imerge->quick_selects);
+        QUICK_RANGE_SELECT *quick;
+        while ((quick= it++))
+        {
+          if (check_if_key_used(table, quick->index, *fields))
+            return 0;
+        }
+        return 1;
+      }
+    }
+
     /* If scanning in clustered key */
     if ((table->file->table_flags() & HA_PRIMARY_KEY_IN_READ_INDEX) &&
 	table->primary_key < MAX_KEY)