Fixed bug #26159.

A wrong order of statements in QUICK_GROUP_MIN_MAX_SELECT::reset
caused a crash when a query with DISTINCT was executed by a loose scan
for an InnoDB table that had been emptied. 


mysql-test/r/innodb_mysql.result:
  Added a test case for bug #26159.
mysql-test/t/innodb_mysql.test:
  Added a test case for bug #26159.
sql/opt_range.cc:
  Fixed bug #26159.
  A wrong order of statements in QUICK_GROUP_MIN_MAX_SELECT::reset
  caused a crash when a query with DISTINCT was executed by a loose scan
  for an InnoDB table that had been emptied. 
  For an empty table quick_prefix_select->reset() was not called at all
  and thus some important initialization steps were missing.

mysql-test/r/innodb_mysql.result

@@ -383,6 +383,33 @@ EXPLAIN SELECT SQL_BIG_RESULT b, SUM(c) FROM t1 GROUP BY b;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	128	Using filesort
 DROP TABLE t1;
+CREATE TABLE t1 (
+id int NOT NULL,
+name varchar(20) NOT NULL,
+dept varchar(20) NOT NULL,
+age tinyint(3) unsigned NOT NULL,
+PRIMARY KEY (id),
+INDEX (name,dept)
+) ENGINE=InnoDB;
+INSERT INTO t1(id, dept, age, name) VALUES
+(3987, 'cs1', 10, 'rs1'), (3988, 'cs2', 20, 'rs1'), (3995, 'cs3', 10, 'rs2'),
+(3996, 'cs4', 20, 'rs2'), (4003, 'cs5', 10, 'rs3'), (4004, 'cs6', 20, 'rs3'),
+(4011, 'cs7', 10, 'rs4'), (4012, 'cs8', 20, 'rs4'), (4019, 'cs9', 10, 'rs5'),
+(4020, 'cs10', 20, 'rs5'),(4027, 'cs11', 10, 'rs6'),(4028, 'cs12', 20, 'rs6');
+EXPLAIN SELECT DISTINCT t1.name, t1.dept FROM t1 WHERE t1.name='rs5';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	range	name	name	44	NULL	2	Using where; Using index for group-by
+SELECT DISTINCT t1.name, t1.dept FROM t1 WHERE t1.name='rs5';
+name	dept
+rs5	cs10
+rs5	cs9
+DELETE FROM t1;
+EXPLAIN SELECT DISTINCT t1.name, t1.dept FROM t1 WHERE t1.name='rs5';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	range	name	name	44	NULL	2	Using where; Using index for group-by
+SELECT DISTINCT t1.name, t1.dept FROM t1 WHERE t1.name='rs5';
+name	dept
+DROP TABLE t1;
 show variables like 'innodb_rollback_on_timeout';
 Variable_name	Value
 innodb_rollback_on_timeout	OFF

mysql-test/t/innodb_mysql.test

@@ -384,6 +384,32 @@ EXPLAIN SELECT SQL_BIG_RESULT b, SUM(c) FROM t1 GROUP BY b;
 DROP TABLE t1;
 
 
+#
+# Bug#26159: crash for a loose scan of a table that has been emptied 
+#
+
+CREATE TABLE t1 (
+  id int NOT NULL,
+  name varchar(20) NOT NULL,
+  dept varchar(20) NOT NULL,
+  age tinyint(3) unsigned NOT NULL,
+  PRIMARY KEY (id),
+  INDEX (name,dept)
+) ENGINE=InnoDB;
+INSERT INTO t1(id, dept, age, name) VALUES
+  (3987, 'cs1', 10, 'rs1'), (3988, 'cs2', 20, 'rs1'), (3995, 'cs3', 10, 'rs2'),
+  (3996, 'cs4', 20, 'rs2'), (4003, 'cs5', 10, 'rs3'), (4004, 'cs6', 20, 'rs3'),
+  (4011, 'cs7', 10, 'rs4'), (4012, 'cs8', 20, 'rs4'), (4019, 'cs9', 10, 'rs5'),
+  (4020, 'cs10', 20, 'rs5'),(4027, 'cs11', 10, 'rs6'),(4028, 'cs12', 20, 'rs6');
+
+EXPLAIN SELECT DISTINCT t1.name, t1.dept FROM t1 WHERE t1.name='rs5';
+SELECT DISTINCT t1.name, t1.dept FROM t1 WHERE t1.name='rs5';
+DELETE FROM t1;
+EXPLAIN SELECT DISTINCT t1.name, t1.dept FROM t1 WHERE t1.name='rs5';
+SELECT DISTINCT t1.name, t1.dept FROM t1 WHERE t1.name='rs5';
+
+DROP TABLE t1;
+
 --source include/innodb_rollback_on_timeout.inc
 
 --echo End of 5.0 tests

sql/opt_range.cc

@@ -8765,14 +8765,13 @@ int QUICK_GROUP_MIN_MAX_SELECT::reset(void)
   DBUG_ENTER("QUICK_GROUP_MIN_MAX_SELECT::reset");
 
   file->extra(HA_EXTRA_KEYREAD); /* We need only the key attributes */
-  result= file->ha_index_init(index);
-  result= file->index_last(record);
-  if (result == HA_ERR_END_OF_FILE)
-    DBUG_RETURN(0);
-  if (result)
+  if ((result= file->ha_index_init(index)))
     DBUG_RETURN(result);
   if (quick_prefix_select && quick_prefix_select->reset())
     DBUG_RETURN(1);
+  result= file->index_last(record);
+  if (result == HA_ERR_END_OF_FILE)
+    DBUG_RETURN(0);
   /* Save the prefix of the last group. */
   key_copy(last_prefix, record, index_info, group_prefix_len);