BUG#13126: When choosing join order for join with nested joins, don't produce join

orders that cannot be handled by the executioner.


mysql-test/r/bigint.result:
  Added mssing "drop table if exists"
mysql-test/r/join_nested.result:
  Testcase for BUG#13126
mysql-test/t/bigint.test:
  Added mssing "drop table if exists"
mysql-test/t/join_nested.test:
  Testcase for BUG#13126
sql/mysql_priv.h:
  BUG#13126: Added nested_join_map type.
sql/sql_prepare.cc:
  BUG#13126: Don't set NESTED_JOIN::counter to 0 here as it is reset in other place now.
sql/sql_select.cc:
  BUG#13126: When choosing join order for join with nested joins, don't produce join orders
  that the executioner cannot handle. The work is done by check_interleaving_with_nj() and 
  restore_prev_nj_state() functions that are used from the join optimizer to avoid building
  invalid join orders.
sql/sql_select.h:
  BUG#13126: Added JOIN_TAB::embedding_map and JOIN::cur_embedding_map.
sql/table.h:
  BUG#13126: In NESTED_JOIN: added nj_map, added comment about where counter is used.

mysql-test/r/bigint.result

-drop table if exists t1;
+drop table if exists t1, t2;
 select 0,256,00000000000000065536,2147483647,-2147483648,2147483648,+4294967296;
 0	256	00000000000000065536	2147483647	-2147483648	2147483648	4294967296
 0	256	65536	2147483647	-2147483648	2147483648	4294967296

mysql-test/r/join_nested.result

@@ -1403,3 +1403,67 @@ SELECT v2.x FROM v2 JOIN t2 ON e=b JOIN t3 ON e=c JOIN t4 USING(d);
 ERROR 42S22: Unknown column 'v2.x' in 'field list'
 DROP VIEW v1, v2;
 DROP TABLE t1, t2, t3, t4, t5, t6;
+create table t1 (id1 int(11) not null);
+insert into t1 values (1),(2);
+create table t2 (id2 int(11) not null);
+insert into t2 values (1),(2),(3),(4);
+create table t3 (id3 char(16) not null);
+insert into t3 values ('100');
+create table t4 (id2 int(11) not null, id3 char(16));
+create table t5 (id1 int(11) not null, key (id1));
+insert into t5 values (1),(2),(1);
+create view v1 as
+select t4.id3 from t4 join t2 on t4.id2 = t2.id2;
+select t1.id1 from t1 inner join (t3 left join v1 on t3.id3 = v1.id3);
+id1
+1
+2
+drop view v1;
+drop table t1, t2, t3, t4, t5;
+create table t0 (a int);
+insert into t0 values (0),(1),(2),(3);
+create table t1(a int);
+insert into t1 select A.a + 10*(B.a) from t0 A, t0 B;
+create table t2 (a int, b int);
+insert into t2 values (1,1), (2,2), (3,3);
+create table t3(a int, b int, filler char(200), key(a));
+insert into t3 select a,a,'filler' from t1;
+insert into t3 select a,a,'filler' from t1;
+create table t4 like t3;
+insert into t4 select * from t3;
+insert into t4 select * from t3;
+create table t5 like t4;
+insert into t5 select * from t4;
+insert into t5 select * from t4;
+create table t6 like t5;
+insert into t6 select * from t5;
+insert into t6 select * from t5;
+create table t7 like t6;
+insert into t7 select * from t6;
+insert into t7 select * from t6;
+explain select * from t4 join 
+t2 left join (t3 join t5 on t5.a=t3.b) on t3.a=t2.b where t4.a<=>t3.b;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	X	
+1	SIMPLE	t3	ref	a	a	5	test.t2.b	X	
+1	SIMPLE	t5	ref	a	a	5	test.t3.b	X	
+1	SIMPLE	t4	ref	a	a	5	test.t3.b	X	Using where
+explain select * from (t4 join t6 on t6.a=t4.b) right join t3 on t4.a=t3.b
+join t2 left join (t5 join t7 on t7.a=t5.b) on t5.a=t2.b where t3.a<=>t2.b;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	X	
+1	SIMPLE	t3	ref	a	a	5	test.t2.b	X	Using where
+1	SIMPLE	t4	ref	a	a	5	test.t3.b	X	
+1	SIMPLE	t6	ref	a	a	5	test.t4.b	X	
+1	SIMPLE	t5	ref	a	a	5	test.t2.b	X	
+1	SIMPLE	t7	ref	a	a	5	test.t5.b	X	
+explain select * from t2 left join
+(t3 left join (t4 join t6 on t6.a=t4.b) on t4.a=t3.b 
+join t5 on t5.a=t3.b) on t3.a=t2.b;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	X	
+1	SIMPLE	t3	ref	a	a	5	test.t2.b	X	
+1	SIMPLE	t4	ref	a	a	5	test.t3.b	X	
+1	SIMPLE	t6	ref	a	a	5	test.t4.b	X	
+1	SIMPLE	t5	ref	a	a	5	test.t3.b	X	
+drop table t0, t1, t2, t4, t5, t6;

mysql-test/t/bigint.test

@@ -2,7 +2,7 @@
 # Initialize
 
 --disable_warnings
-drop table if exists t1;
+drop table if exists t1, t2;
 --enable_warnings
 
 #

mysql-test/t/join_nested.test

@@ -832,3 +832,71 @@ SELECT v2.x FROM v2 JOIN t2 ON e=b JOIN t3 ON e=c JOIN t4 USING(d);
 
 DROP VIEW v1, v2;
 DROP TABLE t1, t2, t3, t4, t5, t6;
+
+#
+# BUG#13126 -test case from bug report
+#
+create table t1 (id1 int(11) not null); 
+insert into t1 values (1),(2);
+
+create table t2 (id2 int(11) not null);
+insert into t2 values (1),(2),(3),(4);
+
+create table t3 (id3 char(16) not null);
+insert into t3 values ('100');
+
+create table t4 (id2 int(11) not null, id3 char(16));
+
+create table t5 (id1 int(11) not null, key (id1));
+insert into t5 values (1),(2),(1);
+
+create view v1 as
+  select t4.id3 from t4 join t2 on t4.id2 = t2.id2;
+
+select t1.id1 from t1 inner join (t3 left join v1 on t3.id3 = v1.id3);
+
+drop view v1;
+drop table t1, t2, t3, t4, t5;
+
+create table t0 (a int);
+insert into t0 values (0),(1),(2),(3);
+create table t1(a int);
+insert into t1 select A.a + 10*(B.a) from t0 A, t0 B;
+
+create table t2 (a int, b int);
+insert into t2 values (1,1), (2,2), (3,3);
+
+create table t3(a int, b int, filler char(200), key(a));
+insert into t3 select a,a,'filler' from t1;
+insert into t3 select a,a,'filler' from t1;
+
+create table t4 like t3;
+insert into t4 select * from t3;
+insert into t4 select * from t3;
+
+create table t5 like t4;
+insert into t5 select * from t4;
+insert into t5 select * from t4;
+
+create table t6 like t5;
+insert into t6 select * from t5;
+insert into t6 select * from t5;
+
+create table t7 like t6;
+insert into t7 select * from t6;
+insert into t7 select * from t6;
+
+--replace_column 9 X
+explain select * from t4 join 
+  t2 left join (t3 join t5 on t5.a=t3.b) on t3.a=t2.b where t4.a<=>t3.b;
+
+--replace_column 9 X
+explain select * from (t4 join t6 on t6.a=t4.b) right join t3 on t4.a=t3.b
+  join t2 left join (t5 join t7 on t7.a=t5.b) on t5.a=t2.b where t3.a<=>t2.b;
+
+--replace_column 9 X
+explain select * from t2 left join
+  (t3 left join (t4 join t6 on t6.a=t4.b) on t4.a=t3.b 
+   join t5 on t5.a=t3.b) on t3.a=t2.b;
+
+drop table t0, t1, t2, t4, t5, t6;

sql/mysql_priv.h

@@ -44,6 +44,11 @@
 typedef ulonglong table_map;          /* Used for table bits in join */
 typedef Bitmap<64> key_map;           /* Used for finding keys */
 typedef ulong key_part_map;           /* Used for finding key parts */
+/*
+  Used for nested join bits within a scope of a join (applicable to non-unary
+  nested joins that have not been simplified away)
+*/
+typedef ulonglong nested_join_map;
 
 /* query_id */
 typedef ulonglong query_id_t;

sql/sql_prepare.cc

@@ -2105,8 +2105,6 @@ void reinit_stmt_before_use(THD *thd, LEX *lex)
       were closed in the end of previous prepare or execute call.
     */
     tables->table= 0;
-    if (tables->nested_join)
-      tables->nested_join->counter= 0;
 
     if (tables->prep_on_expr)
     {

sql/sql_select.cc

@@ -98,6 +98,12 @@ static COND* substitute_for_best_equal_field(COND *cond,
                                              void *table_join_idx);
 static COND *simplify_joins(JOIN *join, List<TABLE_LIST> *join_list,
                             COND *conds, bool top);
+static bool check_interleaving_with_nj(JOIN_TAB *last, JOIN_TAB *next);
+static void restore_prev_nj_state(JOIN_TAB *last);
+static void reset_nj_counters(List<TABLE_LIST> *join_list);
+static uint build_nj_bitmap_for_tables(JOIN *join, List<TABLE_LIST> *join_list,
+                                       uint first_unused);
+
 static COND *optimize_cond(JOIN *join, COND *conds,
                            List<TABLE_LIST> *join_list,
 			   Item::cond_result *cond_value);
@@ -522,12 +528,14 @@ bool JOIN::test_in_subselect(Item **where)
   return 0;
 }
 
+
 /*
   global select optimisation.
   return 0 - success
          1 - error
   error code saved in field 'error'
 */
+
 int
 JOIN::optimize()
 {
@@ -587,6 +595,7 @@ JOIN::optimize()
 
     /* Convert all outer joins to inner joins if possible */
     conds= simplify_joins(this, join_list, conds, TRUE);
+    build_nj_bitmap_for_tables(this, join_list, 0);
 
     sel->prep_where= conds ? conds->copy_andor_structure(thd) : 0;
 
@@ -699,7 +708,8 @@ JOIN::optimize()
     DBUG_PRINT("error",("Error: make_select() failed"));
     DBUG_RETURN(1);
   }
-
+  
+  reset_nj_counters(join_list);
   make_outerjoin_info(this);
 
   /*
@@ -1961,14 +1971,19 @@ make_join_statistics(JOIN *join, TABLE_LIST *tables, COND *conds,
 	continue;
       }
       outer_join|= table->map;
+      s->embedding_map= 0;
+      for (;embedding; embedding= embedding->embedding)
+        s->embedding_map|= embedding->nested_join->nj_map;
       continue;
     }
     if (embedding)
     {
       /* s belongs to a nested join, maybe to several embedded joins */
+      s->embedding_map= 0;
       do
       {
         NESTED_JOIN *nested_join= embedding->nested_join;
+        s->embedding_map|=nested_join->nj_map;
         s->dependent|= embedding->dep_tables;
         embedding= embedding->embedding;
         outer_join|= nested_join->used_tables;
@@ -3542,6 +3557,8 @@ choose_plan(JOIN *join, table_map join_tables)
   bool straight_join= join->select_options & SELECT_STRAIGHT_JOIN;
   DBUG_ENTER("choose_plan");
 
+  join->cur_embedding_map= 0;
+  reset_nj_counters(join->join_list);
   /*
     if (SELECT_STRAIGHT_JOIN option is set)
       reorder tables so dependent tables come after tables they depend 
@@ -4022,7 +4039,9 @@ best_extension_by_limited_search(JOIN      *join,
   for (JOIN_TAB **pos= join->best_ref + idx ; (s= *pos) ; pos++)
   {
     table_map real_table_bit= s->table->map;
-    if ((remaining_tables & real_table_bit) && !(remaining_tables & s->dependent))
+    if ((remaining_tables & real_table_bit) && 
+        !(remaining_tables & s->dependent) && 
+        (!idx || !check_interleaving_with_nj(join->positions[idx-1].table, s)))
     {
       double current_record_count, current_read_time;
 
@@ -4038,6 +4057,7 @@ best_extension_by_limited_search(JOIN      *join,
       {
         DBUG_EXECUTE("opt", print_plan(join, read_time, record_count, idx,
                                        "prune_by_cost"););
+        restore_prev_nj_state(s);
         continue;
       }
 
@@ -4066,6 +4086,7 @@ best_extension_by_limited_search(JOIN      *join,
         {
           DBUG_EXECUTE("opt", print_plan(join, read_time, record_count, idx,
                                          "pruned_by_heuristic"););
+          restore_prev_nj_state(s);
           continue;
         }
       }
@@ -4100,9 +4121,11 @@ best_extension_by_limited_search(JOIN      *join,
                  sizeof(POSITION) * (idx + 1));
           join->best_read= current_read_time - 0.001;
         }
-        DBUG_EXECUTE("opt",
-                     print_plan(join, current_read_time, current_record_count, idx, "full_plan"););
+        DBUG_EXECUTE("opt", print_plan(join, current_read_time, 
+                                       current_record_count, idx, 
+                                       "full_plan"););
       }
+      restore_prev_nj_state(s);
     }
   }
   DBUG_VOID_RETURN;
@@ -4147,7 +4170,8 @@ find_best(JOIN *join,table_map rest_tables,uint idx,double record_count,
   for (JOIN_TAB **pos=join->best_ref+idx ; (s=*pos) ; pos++)
   {
     table_map real_table_bit=s->table->map;
-    if ((rest_tables & real_table_bit) && !(rest_tables & s->dependent))
+    if ((rest_tables & real_table_bit) && !(rest_tables & s->dependent) &&
+        (!idx|| !check_interleaving_with_nj(join->positions[idx-1].table, s)))
     {
       double best,best_time,records;
       best=best_time=records=DBL_MAX;
@@ -4485,10 +4509,10 @@ find_best(JOIN *join,table_map rest_tables,uint idx,double record_count,
 	  join->unit->select_limit_cnt >= records)
 	join->sort_by_table= (TABLE*) 1;	// Must use temporary table
 
-     /*
+      /*
 	Go to the next level only if there hasn't been a better key on
 	this level! This will cut down the search for a lot simple cases!
-       */
+      */
       double current_record_count=record_count*records;
       double current_read_time=read_time+best;
       if (best_record_count > current_record_count ||
@@ -4509,6 +4533,7 @@ find_best(JOIN *join,table_map rest_tables,uint idx,double record_count,
           return;
 	swap_variables(JOIN_TAB*, join->best_ref[idx], *pos);
       }
+      restore_prev_nj_state(s);
       if (join->select_options & SELECT_STRAIGHT_JOIN)
 	break;				// Don't test all combinations
     }
@@ -5094,7 +5119,7 @@ add_found_match_trig_cond(JOIN_TAB *tab, COND *cond, JOIN_TAB *root_tab)
     This function can be called only after the execution plan
     has been chosen.
 */
- 
+
 static void
 make_outerjoin_info(JOIN *join)
 {
@@ -7255,11 +7280,11 @@ propagate_cond_constants(THD *thd, I_List<COND_CMP> *save_list,
     ascent all attributes are calculated, all outer joins that can be
     converted are replaced and then all unnecessary braces are removed.
     As join list contains join tables in the reverse order sequential
-    elimination of outer joins does not requite extra recursive calls.
+    elimination of outer joins does not require extra recursive calls.
 
   EXAMPLES
     Here is an example of a join query with invalid cross references:
-      SELECT * FROM t1 LEFT JOIN t2 ON t2.a=t3.a LEFT JOIN ON  t3.b=t1.b 
+      SELECT * FROM t1 LEFT JOIN t2 ON t2.a=t3.a LEFT JOIN t3 ON t3.b=t1.b 
      
   RETURN VALUE
     The new condition, if success
@@ -7416,7 +7441,210 @@ simplify_joins(JOIN *join, List<TABLE_LIST> *join_list, COND *conds, bool top)
   }
   DBUG_RETURN(conds); 
 }
-        
+
+
+/*
+  Assign each nested join structure a bit in nested_join_map
+
+  SYNOPSIS
+    build_nj_bitmap_for_tables()
+      join          Join being processed
+      join_list     List of tables
+      first_unused  Number of first unused bit in nested_join_map before the
+                    call
+
+  DESCRIPTION
+    Assign each nested join structure (except for unary nested joins, see
+    below) a bit in nested_join_map.
+
+  NOTE
+    This function is called after simplify_joins(), when there are no
+    redundant nested joins, #non_unary_nested_joins <= #tables_in_join so we
+    will not run out of bits in nested_join_map.
+
+  RETURN
+    First unused bit in nested_join_map after the call.
+*/
+
+static uint build_nj_bitmap_for_tables(JOIN *join, List<TABLE_LIST> *join_list,
+                                       uint first_unused)
+{
+  List_iterator<TABLE_LIST> li(*join_list);
+  TABLE_LIST *table;
+  DBUG_ENTER("build_nj_bitmap_for_tables");
+  while ((table= li++))
+  {
+    NESTED_JOIN *nested_join;
+    if ((nested_join= table->nested_join))
+    {
+      /*
+        It is guaranteed by simplify_joins() function that a nested join
+        that has only one child represents a single table VIEW (and a child
+        is an underlying table). We don't assign a bit to the nested join
+        because 
+        1. it is redundant (a "sequence" of one table cannot be interleaved 
+            with anything)
+        2. we could run out bits in nested_join_map otherwise.
+      */
+      if (nested_join->join_list.elements != 1)
+      {
+        nested_join->nj_map= 1 << first_unused++;
+        first_unused= build_nj_bitmap_for_tables(join, &nested_join->join_list,
+                                                 first_unused);
+      }
+    }
+  }
+  DBUG_RETURN(first_unused);
+}
+
+
+/*
+  Set NESTED_JOIN::counter=0 in all nested joins in passed list
+
+  SYNOPSIS
+    reset_nj_counters()
+      join_list  List of nested joins to process. It may also contain base
+                 tables which will be ignored.
+
+  DESCRIPTION
+    Recursively set NESTED_JOIN::counter=0 for all nested joins contained in
+    the passed join_list.
+*/
+
+static void reset_nj_counters(List<TABLE_LIST> *join_list)
+{
+  List_iterator<TABLE_LIST> li(*join_list);
+  TABLE_LIST *table;
+  DBUG_ENTER("reset_nj_counters");
+  while ((table= li++))
+  {
+    NESTED_JOIN *nested_join;
+    if ((nested_join= table->nested_join))
+    {
+      nested_join->counter= 0;
+      reset_nj_counters(&nested_join->join_list);
+    }
+  }
+  DBUG_VOID_RETURN;
+}
+
+
+/*
+  Check interleaving with an inner tables of an outer join for extension table 
+
+  SYNOPSIS
+    check_interleaving_with_nj()
+      join       Join being processed
+      last_tab   Last table in current partial join order (this function is
+                 not called for empty partial join orders)
+      next_tab   Table we're going to extend the current partial join with
+
+  DESCRIPTION
+    Check if table next_tab can be added to current partial join order, and 
+    if yes, record that it has been added.
+
+    The function assumes that both current partial join order and its
+    extension with next_tab are valid wrt table dependencies.
+
+  NOTE
+    The nested joins aspect of information about current partial join order is 
+    stored in join->cur_embedding_map and
+    {each_join_table}->pos_in_table_list (->embedding)+ ->nested_join->counter
+    Joins optimizer calls check_interleaving_with_nj() and 
+    restore_prev_nj_state() to update this info and avoid constructing invalid 
+    join orders. There is no need for any initialization of 
+    {each_join_table}->...->counter  before the join optimizer run.
+
+  IMPLEMENTATION
+    The nested [outer] joins executioner algorithm imposes these limitations 
+    on join order:
+    1. "Outer tables first" -  any "outer" table must be before any 
+        corresponding "inner" table.
+    2. "No interleaving" - tables inside a nested join must form a continuous
+       sequence in join order (i.e. the sequence must not be interrupted by 
+       tables that are outside of this nested join).
+
+    #1 is checked elsewhere, this function checks #2 provided that #1 has been
+    already checked.
+
+    WHY NEED NON-INTERLEAVING
+    Consider an example: 
+     
+     select * from t0 join t1 left join (t2 join t3) on cond1
+    
+    The join order "t1 t2 t0 t3" is invalid:
+
+    table t0 is outside of the nested join, so WHERE condition for t0 is
+    attached directly to t0 (without triggers, and it may be used to access
+    t0). Applying WHERE(t0) to (t2,t0,t3) record is invalid as we may miss
+    combinations of (t1, t2, t3) that satisfy condition cond1, and produce a
+    null-complemented (t1, t2.NULLs, t3.NULLs) row, which should not have
+    been produced.
+    
+    If table t0 is not between t2 and t3, the problem doesn't exist:
+    * If t0 is located after (t2,t3), WHERE(t0) is applied after nested join
+      processing has finished.
+    * If t0 is located before (t2,t3), predicates like WHERE_cond(t0, t2) are
+      wrapped into condition triggers, which takes care of correct nested
+      join processing.
+    
+  RETURN
+    FALSE  Join order extended, nested joins info about current join order
+           (see NOTE section) updated.
+    TRUE   Requested join order extension not allowed.
+*/
+
+static bool check_interleaving_with_nj(JOIN_TAB *last, JOIN_TAB *next)
+{
+  TABLE_LIST *next_emb= next->table->pos_in_table_list->embedding;
+  JOIN *join= last->join;
+
+  if (join->cur_embedding_map & ~next->embedding_map)
+    return TRUE;
+   
+  for (;next_emb; next_emb= next_emb->embedding)
+  {
+    next_emb->nested_join->counter++;
+    if (next_emb->nested_join->counter == 1)
+    {
+      /* next_emb is a first table inside a nested join */
+      join->cur_embedding_map |= next_emb->nested_join->nj_map;
+    }
+    if (next_emb->nested_join->join_list.elements !=
+        next_emb->nested_join->counter)
+      break;
+    join->cur_embedding_map &= ~next_emb->nested_join->nj_map;
+  }
+  return FALSE;
+}
+
+
+/*
+  Nested joins perspective: Remove the last table from the join order
+
+  SYNOPSIS
+    restore_prev_nj_state()
+      last  join table to remove, it is assumed to be the last in current 
+            partial join order.
+     
+  DESCRIPTION
+    Remove the last table from the partial join order and update the nested
+    joins counters and join->cur_embedding_map. It is ok to call this 
+    function for the first table in join order (for which 
+    check_interleaving_with_nj has not been called)
+*/
+
+static void restore_prev_nj_state(JOIN_TAB *last)
+{
+  TABLE_LIST *last_emb= last->table->pos_in_table_list->embedding;
+  JOIN *join= last->join;
+  while (last_emb && !(--last_emb->nested_join->counter))
+  {
+    join->cur_embedding_map &= last_emb->nested_join->nj_map;
+    last_emb= last_emb->embedding;
+  }
+}
+
 
 static COND *
 optimize_cond(JOIN *join, COND *conds, List<TABLE_LIST> *join_list,

sql/sql_select.h

@@ -136,7 +136,9 @@ typedef struct st_join_table {
   TABLE_REF	ref;
   JOIN_CACHE	cache;
   JOIN		*join;
-
+  /* Bitmap of nested joins this table is part of */
+  nested_join_map embedding_map;
+  
   void cleanup();
 } JOIN_TAB;
 
@@ -193,6 +195,13 @@ class JOIN :public Sql_alloc
   */
   ha_rows  fetch_limit;
   POSITION positions[MAX_TABLES+1],best_positions[MAX_TABLES+1];
+  
+  /* 
+    Bitmap of nested joins embedding the position at the end of the current 
+    partial join (valid only during join optimizer run).
+  */
+  nested_join_map cur_embedding_map;
+
   double   best_read;
   List<Item> *fields;
   List<Cached_item> group_fields, group_fields_cache;

sql/table.h

@@ -757,7 +757,15 @@ typedef struct st_nested_join
   table_map         used_tables;     /* bitmap of tables in the nested join */
   table_map         not_null_tables; /* tables that rejects nulls           */
   struct st_join_table *first_nested;/* the first nested table in the plan  */
-  uint              counter;         /* to count tables in the nested join  */
+  /* 
+    Used to count tables in the nested join in 2 isolated places:
+    1. In make_outerjoin_info(). 
+    2. check_interleaving_with_nj/restore_prev_nj_state (these are called
+       by the join optimizer. 
+    Before each use the counters are zeroed by reset_nj_counters.
+  */
+  uint              counter;
+  nested_join_map   nj_map;          /* Bit used to identify this nested join*/
 } NESTED_JOIN;