MDEV-10325: Queries examines all rows of a tables when it should not

The problem was introduced by 1859caf60b:
  MDEV-10175: range optimizer calls records_in_range() for full extended keys

  Make the range optimizer not call records_in_range() when it would
  not give any benefit.

that patch used an incorrect way to check for full extended key. Now fixing
the check.

mysql-test/r/innodb_ext_key.result

@@ -1040,5 +1040,29 @@ a
 1
 drop table t1, t2;
 set optimizer_switch=@save_optimizer_switch;
+# 
+# MDEV-10325: Queries examines all rows of a tables when it should not
+# 
+create table t0 (a int);
+insert into t0 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+create table t1 (
+pk int not null,
+col1 varchar(32),
+filler varchar(100),
+key idx1(col1(10)),
+primary key (pk)
+)engine=innodb;
+insert into t1 
+select
+A.a + 10*B.a + 100*C.a,
+concat('1234567890-', 1000+ A.a + 10*B.a + 100*C.a),
+repeat('filler-data-', 4)
+from 
+t0 A, t0 B, t0 C;
+# The following must use type=ALL (and NOT type=ref, rows=1)
+explain select * from t1 where col1='1234567890-a';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	idx1	NULL	NULL	NULL	#	Using where
+drop table t0,t1;
 set optimizer_switch=@save_ext_key_optimizer_switch;
 SET SESSION STORAGE_ENGINE=DEFAULT;

mysql-test/t/innodb_ext_key.test

@@ -693,5 +693,33 @@ drop table t1, t2;
 
 set optimizer_switch=@save_optimizer_switch;
 
+--echo # 
+--echo # MDEV-10325: Queries examines all rows of a tables when it should not
+--echo # 
+create table t0 (a int);
+insert into t0 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+
+create table t1 (
+  pk int not null,
+  col1 varchar(32),
+  filler varchar(100),
+  key idx1(col1(10)),
+  primary key (pk)
+)engine=innodb;
+
+insert into t1 
+select
+  A.a + 10*B.a + 100*C.a,
+  concat('1234567890-', 1000+ A.a + 10*B.a + 100*C.a),
+  repeat('filler-data-', 4)
+from 
+  t0 A, t0 B, t0 C;
+
+--echo # The following must use type=ALL (and NOT type=ref, rows=1)
+--replace_column 9 #
+explain select * from t1 where col1='1234567890-a';
+
+drop table t0,t1;
+
 set optimizer_switch=@save_ext_key_optimizer_switch;
 SET SESSION STORAGE_ENGINE=DEFAULT;

sql/opt_range_mrr.cc

@@ -278,14 +278,14 @@ walk_up_n_right:
        (1) - range analysis is used for estimating condition selectivity
        (2) - This is a unique key, and we have conditions for all its 
              user-defined key parts.
-       (3) - The table uses extended keys, and we have conditions for 
+       (3) - The table uses extended keys, this key covers all components,
-             all key parts.
+             and we have conditions for all key parts.
     */
     if (!(cur->min_key_flag & ~NULL_RANGE) && !cur->max_key_flag &&
         (!key_info ||   // (1)
          ((uint)key_tree->part+1 == key_info->user_defined_key_parts && // (2)
 	  key_info->flags & HA_NOSAME) ||                               // (2)
-         (seq->param->table->s->use_ext_keys &&               // (3)
+         ((key_info->flags & HA_EXT_NOSAME) &&                 // (3)
           (uint)key_tree->part+1 == key_info->ext_key_parts)  // (3)
         ) &&
         range->start_key.length == range->end_key.length &&