Fix bug lp:869036

Apart from the fix, the patch also adds few more unrelated test
cases for partial matching, and fixes few typos.

Analysis:
This bug uncovered that partial matching via rowid intersection
didn't handle the case when:
- the left IN argument has some NULLs,
- there are no non-null value matches, and there is no non-null
  column,
- the subquery columns that are not covered with the NULLs in
  the left IN argument contain at least one row, such that it
  has NULL values in all columns where the left IN operand has
  no NULLs.
In this case there is a partial match.

In addition the analysis of the related code uncovered incorrect
handling of few other related cases.

Solution:
The solution for the bug is to check if there exists a row with
NULLs in all columns other than the ones having NULL in the
let IN operand.

The check is implemented via checking whether the bitmaps that
store NULL information in class Ordered_key have a non-empty
intersection for the relevant columns.

The intersection itself is implemented via the function
bitmap_exists_intersection() in my_bitmap.c.

1 files changed, 10 insertions, 3 deletions

diff --git a/sql/item_subselect.h b/sql/item_subselect.h
index 2012306c0f7..28ce0061729 100644
--- a/sql/item_subselect.h
+++ b/sql/item_subselect.h
@@ -999,7 +999,7 @@ protected:
 
 
 /*
-  Distinguish the type od (0-based) row numbers from the type of the index into
+  Distinguish the type of (0-based) row numbers from the type of the index into
   an array of row numbers.
 */
 typedef ha_rows rownum_t;
@@ -1075,9 +1075,9 @@ protected:
   /* Count of NULLs per column. */
   ha_rows null_count;
   /* The row number that contains the first NULL in a column. */
-  ha_rows min_null_row;
+  rownum_t min_null_row;
   /* The row number that contains the last NULL in a column. */
-  ha_rows max_null_row;
+  rownum_t max_null_row;
 
 protected:
   bool alloc_keys_buffers();
@@ -1110,6 +1110,10 @@ public:
     DBUG_ASSERT(i < key_column_count);
     return key_columns[i]->field->field_index;
   }
+  rownum_t get_min_null_row() { return min_null_row; }
+  rownum_t get_max_null_row() { return max_null_row; }
+  MY_BITMAP * get_null_key() { return &null_key; }
+  ha_rows get_null_count() { return null_count; }
   /*
     Get the search key element that corresponds to the i-th key part of this
     index.
@@ -1280,6 +1284,8 @@ protected:
   Ordered_key **merge_keys;
   /* The number of elements in merge_keys. */
   uint merge_keys_count;
+  /* The NULL bitmaps of merge keys.*/
+  MY_BITMAP   **null_bitmaps;
   /*
     An index on all non-NULL columns of 'tmp_table'. The index has the
     logical form: <[v_i1 | ... | v_ik], rownum>. It allows to find the row
@@ -1305,6 +1311,7 @@ protected:
   static int cmp_keys_by_cur_rownum(void *arg, uchar *k1, uchar *k2);
 
   bool test_null_row(rownum_t row_num);
+  bool exists_complementing_null_row(MY_BITMAP *keys_to_complement);
   bool partial_match();
 public:
   subselect_rowid_merge_engine(THD *thd_arg,