MDEV-20740: Odd computations in calculate_cond_selectivity_for_table

Make SEL_ARG graph traversal code in sel_arg_range_seq_next() set
max_key_parts first.

(Pushing to 10.4 first)

mysql-test/main/index_intersect_innodb.result

@@ -470,17 +470,17 @@ EXPLAIN
 SELECT * FROM City
 WHERE ID BETWEEN 501 AND 1000 AND Population > 700000 AND Country LIKE 'C%';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	City	index_merge	PRIMARY,Population,Country	PRIMARY,Country,Population	4,7,4	NULL	#	Using sort_intersect(PRIMARY,Country,Population); Using where
+1	SIMPLE	City	index_merge	PRIMARY,Population,Country	PRIMARY,Population,Country	4,4,7	NULL	#	Using sort_intersect(PRIMARY,Population,Country); Using where
 EXPLAIN
 SELECT * FROM City
 WHERE ID BETWEEN 1 AND 500 AND Population > 700000 AND Country LIKE 'C%';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	City	index_merge	PRIMARY,Population,Country	PRIMARY,Country,Population	4,7,4	NULL	#	Using sort_intersect(PRIMARY,Country,Population); Using where
+1	SIMPLE	City	index_merge	PRIMARY,Population,Country	PRIMARY,Population,Country	4,4,7	NULL	#	Using sort_intersect(PRIMARY,Population,Country); Using where
 EXPLAIN
 SELECT * FROM City 
 WHERE ID BETWEEN 2001 AND 2500 AND Population > 300000 AND Country LIKE 'H%';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	City	index_merge	PRIMARY,Population,Country	PRIMARY,Country	4,7	NULL	#	Using sort_intersect(PRIMARY,Country); Using where
+1	SIMPLE	City	range	PRIMARY,Population,Country	Country	7	NULL	#	Using index condition; Using where
 EXPLAIN
 SELECT * FROM City 
 WHERE ID BETWEEN 3701 AND 4000 AND Population > 1000000
@@ -724,7 +724,7 @@ EXPLAIN
 SELECT * FROM City
 WHERE ID BETWEEN 1 AND 500 AND Population > 700000 AND Country LIKE 'C%';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	City	index_merge	PRIMARY,Population,Country	PRIMARY,Country,Population	4,7,4	NULL	#	Using sort_intersect(PRIMARY,Country,Population); Using where
+1	SIMPLE	City	index_merge	PRIMARY,Population,Country	PRIMARY,Population,Country	4,4,7	NULL	#	Using sort_intersect(PRIMARY,Population,Country); Using where
 EXPLAIN
 SELECT * FROM City 
 WHERE ID BETWEEN 3001 AND 4000 AND Population > 600000

sql/opt_range.cc

@@ -315,7 +315,7 @@ class PARAM : public RANGE_OPT_PARAM
   */
   key_map possible_keys;
   longlong baseflag;
-  uint max_key_part, range_count;
+  uint max_key_parts, range_count;
 
   bool quick;				// Don't calulate possible keys
 
@@ -7387,7 +7387,7 @@ static TRP_RANGE *get_key_scans_params(PARAM *param, SEL_TREE *tree,
         index_scan->idx= idx;
         index_scan->keynr= keynr;
         index_scan->key_info= &param->table->key_info[keynr];
-        index_scan->used_key_parts= param->max_key_part+1;
+        index_scan->used_key_parts= param->max_key_parts;
         index_scan->range_count= param->range_count;
         index_scan->records= found_records;
         index_scan->sel_arg= key;
@@ -11042,7 +11042,7 @@ ha_rows check_quick_select(PARAM *param, uint idx, bool index_only,
   seq.start= tree;
 
   param->range_count=0;
-  param->max_key_part=0;
+  param->max_key_parts=0;
 
   seq.is_ror_scan= TRUE;
   if (file->index_flags(keynr, 0, TRUE) & HA_KEY_SCAN_NOT_ROR)
@@ -11055,9 +11055,13 @@ ha_rows check_quick_select(PARAM *param, uint idx, bool index_only,
   *mrr_flags|= HA_MRR_NO_ASSOCIATION | HA_MRR_SORTED;
 
   bool pk_is_clustered= file->primary_key_is_clustered();
+  // TODO: param->max_key_parts holds 0 now, and not the #keyparts used.
+  // Passing wrong second argument to index_flags() makes no difference for
+  // most storage engines but might be an issue for MyRocks with certain
+  // datatypes.
   if (index_only && 
-      (file->index_flags(keynr, param->max_key_part, 1) & HA_KEYREAD_ONLY) &&
-      !(file->index_flags(keynr, param->max_key_part, 1) & HA_CLUSTERED_INDEX))
+      (file->index_flags(keynr, param->max_key_parts, 1) & HA_KEYREAD_ONLY) &&
+      !(file->index_flags(keynr, param->max_key_parts, 1) & HA_CLUSTERED_INDEX))
      *mrr_flags |= HA_MRR_INDEX_ONLY;
   
   if (param->thd->lex->sql_command != SQLCOM_SELECT)
@@ -11088,7 +11092,7 @@ ha_rows check_quick_select(PARAM *param, uint idx, bool index_only,
     if (update_tbl_stats)
     {
       param->table->quick_keys.set_bit(keynr);
-      param->table->quick_key_parts[keynr]= param->max_key_part+1;
+      param->table->quick_key_parts[keynr]= param->max_key_parts;
       param->table->quick_n_ranges[keynr]= param->range_count;
       param->table->quick_condition_rows=
         MY_MIN(param->table->quick_condition_rows, rows);

sql/opt_range_mrr.cc

@@ -247,6 +247,7 @@ bool sel_arg_range_seq_next(range_seq_t rseq, KEY_MULTI_RANGE *range)
   uint min_key_length= (uint)(cur->min_key - seq->param->min_key);
   
   range->ptr= (char*)(intptr)(key_tree->part);
+  uint max_key_parts;
   if (cur->min_key_flag & GEOM_FLAG)
   {
     range->range_flag= cur->min_key_flag;
@@ -256,9 +257,11 @@ bool sel_arg_range_seq_next(range_seq_t rseq, KEY_MULTI_RANGE *range)
     range->start_key.length= min_key_length;
     range->start_key.keypart_map= make_prev_keypart_map(cur->min_key_parts);
     range->start_key.flag=  (ha_rkey_function) (cur->min_key_flag ^ GEOM_FLAG);
+    max_key_parts= cur->min_key_parts;
   }
   else
   {
+    max_key_parts= MY_MAX(cur->min_key_parts, cur->max_key_parts);
     range->range_flag= cur->min_key_flag | cur->max_key_flag;
     
     range->start_key.key=    seq->param->min_key;
@@ -336,7 +339,7 @@ bool sel_arg_range_seq_next(range_seq_t rseq, KEY_MULTI_RANGE *range)
     }
   }
   seq->param->range_count++;
-  seq->param->max_key_part=MY_MAX(seq->param->max_key_part,key_tree->part);
+  seq->param->max_key_parts= MY_MAX(seq->param->max_key_parts, max_key_parts);
   return 0;
 }