BUG#32772: partition crash 1: enum column

The bug was that for ordered index scans, ha_partition::index_init() did
not put index columns into table->read_set if the underlying storage 
engine did not have HA_PARTIAL_COLUMN_READ flag. 
This was causing assertion failure when handle_ordered_index_scan() tried
to sort the records according to index order.

Fixed by making ha_partition::index_init() put index columns into table->read_set
for all ordered scans. 

mysql-test/r/partition.result

@@ -1290,4 +1290,17 @@ create table t1
 partition by key(s1) partitions 3;
 insert into t1 values (null,null);
 drop table t1;
+create table t1 (
+c0 int,
+c1 bigint,
+c2 set('sweet'),
+key (c2,c1,c0), 
+key(c0)
+) engine=myisam partition by hash (month(c0)) partitions 5;
+insert ignore into t1 set c0 = -6502262, c1 = 3992917, c2 = 35019;
+insert ignore into t1 set c0 = 241221, c1 = -6862346, c2 = 56644;
+select c1 from t1 group by (select c0 from t1 limit 1);
+c1
+-6862346
+drop table t1;
 End of 5.1 tests

mysql-test/t/partition.test

@@ -1531,4 +1531,24 @@ while ($cnt)
 --enable_query_log
 
 drop table t1;
+
+#
+# BUG#32272: partition crash 1: enum column
+#
+create table t1 (
+  c0 int,
+  c1 bigint,
+  c2 set('sweet'),
+  key (c2,c1,c0), 
+  key(c0)
+) engine=myisam partition by hash (month(c0)) partitions 5;
+
+--disable_warnings
+insert ignore into t1 set c0 = -6502262, c1 = 3992917, c2 = 35019;
+insert ignore into t1 set c0 = 241221, c1 = -6862346, c2 = 56644;
+--enable_warnings
+# This must not fail assert:
+select c1 from t1 group by (select c0 from t1 limit 1);
+drop table t1;
+
 --echo End of 5.1 tests

sql/ha_partition.cc

@@ -3413,14 +3413,17 @@ int ha_partition::index_init(uint inx, bool sorted)
   */
   if (m_lock_type == F_WRLCK)
     bitmap_union(table->read_set, &m_part_info->full_part_field_set);
-  else if (sorted && m_table_flags & HA_PARTIAL_COLUMN_READ)
+  else if (sorted)
   {
     /*
-      An ordered scan is requested and necessary fields aren't in read_set.
-      This may happen e.g. with SELECT COUNT(*) FROM t1. We must ensure
-      that all fields of current key are included into read_set, as
-      partitioning requires them for sorting
-      (see ha_partition::handle_ordered_index_scan).
+      An ordered scan is requested. We must make sure all fields of the 
+      used index are in the read set, as partitioning requires them for
+      sorting (see ha_partition::handle_ordered_index_scan).
+
+      The SQL layer may request an ordered index scan without having index
+      fields in the read set when
+       - it needs to do an ordered scan over an index prefix.
+       - it evaluates ORDER BY with SELECT COUNT(*) FROM t1.
 
       TODO: handle COUNT(*) queries via unordered scan.
     */