Fix bug lp:825095

Analysis:
Partial matching is used even when there are no NULLs in
a materialized subquery, as long as the left NOT IN operand
may contain NULL values.

This case was not handled correctly in two different places.
First, the implementation of parital matching did not clear
the set of matching columns when the merge process advanced
to the next row.

Second, there is no need to perform partial matching at all
when the left operand has no NULLs.

Solution:
First fix subselect_rowid_merge_engine::partial_match() to
properly cleanup the bitmap of matching keys when advancing
to the next row.

Second, change subselect_partial_match_engine::exec() so
that when the materialized subquery doesn't contain any
NULLs, and the left operand of [NOT] IN doesn't contain
NULLs either, the method returns without doing any
unnecessary partial matching. The correct result in this
case is in Item::in_value.

1 files changed, 10 insertions, 4 deletions

diff --git a/sql/item_subselect.h b/sql/item_subselect.h
index 2c1e3bddb2d..f9e7a5ef568 100644
--- a/sql/item_subselect.h
+++ b/sql/item_subselect.h
@@ -870,7 +870,7 @@ public:
       tmp_table(NULL), is_materialized(FALSE), materialize_engine(old_engine),
       materialize_join(NULL),  semi_join_conds(NULL), lookup_engine(NULL),
       count_partial_match_columns(0), count_null_only_columns(0),
-      strategy(UNDEFINED)
+      count_columns_with_nulls(0), strategy(UNDEFINED)
   {}
   ~subselect_hash_sj_engine();
 
@@ -908,6 +908,7 @@ protected:
   MY_BITMAP partial_match_key_parts;
   uint count_partial_match_columns;
   uint count_null_only_columns;
+  uint count_columns_with_nulls;
   /* Possible execution strategies that can be used to compute hash semi-join.*/
   enum exec_strategy {
     UNDEFINED,
@@ -1145,6 +1146,7 @@ protected:
     guaranteed partial match.
   */
   bool has_covering_null_columns;
+  uint count_columns_with_nulls;
 
 protected:
   virtual bool partial_match()= 0;
@@ -1155,7 +1157,8 @@ public:
                                  select_result_interceptor *result_arg,
                                  List<Item> *equi_join_conds_arg,
                                  bool has_covering_null_row_arg,
-                                 bool has_covering_null_columns_arg);
+                                 bool has_covering_null_columns_arg,
+                                 uint count_columns_with_nulls_arg);
   int prepare() { return 0; }
   int exec();
   void fix_length_and_dec(Item_cache**) {}
@@ -1245,13 +1248,15 @@ public:
                                TABLE *tmp_table_arg, uint merge_keys_count_arg,
                                bool has_covering_null_row_arg,
                                bool has_covering_null_columns_arg,
+                               uint count_columns_with_nulls_arg,
                                Item_subselect *item_arg,
                                select_result_interceptor *result_arg,
                                List<Item> *equi_join_conds_arg)
     :subselect_partial_match_engine(thd_arg, engine_arg, tmp_table_arg,
                                     item_arg, result_arg, equi_join_conds_arg,
                                     has_covering_null_row_arg,
-                                    has_covering_null_columns_arg),
+                                    has_covering_null_columns_arg,
+                                    count_columns_with_nulls_arg),
     merge_keys_count(merge_keys_count_arg), non_null_key(NULL)
   {}
   ~subselect_rowid_merge_engine();
@@ -1272,7 +1277,8 @@ public:
                               select_result_interceptor *result_arg,
                               List<Item> *equi_join_conds_arg,
                               bool has_covering_null_row_arg,
-                              bool has_covering_null_columns_arg);
+                              bool has_covering_null_columns_arg,
+                              uint count_columns_with_nulls_arg);
   void cleanup();
   virtual enum_engine_type engine_type() { return TABLE_SCAN_ENGINE; }
 };