Bug#18383840: SEGV IN MEMCPY(), HA_PARTITION::POSITION

post-push fix for:
Regression from bug#18167648: WRONG RESULTS WITH PARTITIONING,
INDEX_MERGE MYISAM AND NO PK INNODB

The priority queue is setup in ha_partition::index_init() and also sets
m_sec_sort_by_rowid. But in case the index scan is only done on one
partition, due to pruning, the priority queue will not be used and
the ref will not be copied into the priority queue. So only checking
m_sec_sort_by_rowid is not enough to ensure that the ref is
accessible.

Fixed by checking that ordered scan is used.

Author: Mattias Jonsson

mysql-test/r/partition_index_innodb.result

@@ -34,6 +34,12 @@ a	b	c
 2	2	17
 2	2	20
 2	2	25
+EXPLAIN PARTITIONS SELECT a,b,c FROM t1 WHERE a = 2 AND b = 2 AND c IN (13,25,28);
+id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	p1	index_merge	a,b	a,b	3,3	NULL	1	Using intersect(a,b); Using where
+SELECT a,b,c FROM t1 WHERE a = 2 AND b = 2 AND c IN (13,25,28);
+a	b	c
+2	2	25
 SET SESSION optimizer_switch="index_merge_intersection=off";
 SELECT a,b,c FROM t1 WHERE b = 2 AND a = 2 AND  c > 0 AND c < 100;
 a	b	c

mysql-test/t/partition_index_innodb.test

@@ -62,6 +62,8 @@ SELECT TRACE FROM INFORMATION_SCHEMA.OPTIMIZER_TRACE;
 # No more match...
 
 SELECT a,b,c FROM t1 WHERE b = 2 AND a = 2 AND  c > 0 AND c < 100;
+EXPLAIN PARTITIONS SELECT a,b,c FROM t1 WHERE a = 2 AND b = 2 AND c IN (13,25,28);
+SELECT a,b,c FROM t1 WHERE a = 2 AND b = 2 AND c IN (13,25,28);
 SET SESSION optimizer_switch="index_merge_intersection=off";
 SELECT a,b,c FROM t1 WHERE b = 2 AND a = 2 AND  c > 0 AND c < 100;
 EXPLAIN SELECT a,b,c FROM t1 WHERE b = 2 AND a = 2 AND  c > 0 AND c < 100;

sql/ha_partition.cc

@@ -4785,9 +4785,13 @@ void ha_partition::position(const uchar *record)
   DBUG_ENTER("ha_partition::position");
 
   int2store(ref, m_last_part);
-  if (m_sec_sort_by_rowid)
+  /*
+    If m_sec_sort_by_rowid is set, then the ref is already stored in the
+    priority queue (m_queue) when doing ordered scans.
+  */
+  if (m_sec_sort_by_rowid && m_ordered_scan_ongoing)
   {
-    DBUG_ASSERT(m_ordered_scan_ongoing);
+    DBUG_ASSERT(m_queue.elements);
     DBUG_ASSERT(m_ordered_rec_buffer);
     DBUG_ASSERT(!m_curr_key_info[1]);
     /* We already have the ref. */