Bug#16540042: WRONG QUERY RESULT WHEN USING RANGE OVER

              PARTIAL INDEX

Consider the following table definition:

CREATE TABLE t (
  my_col CHAR(10),
  ...
  INDEX my_idx (my_col(1))
)

The my_idx index is not able to distinguish between rows with
equal first-character my_col-values (e.g. "f", "foo", "fee").

Prior to this CS, the range optimizer would translate

"WHERE my_col NOT IN ('f', 'h')" into (optimizer trace syntax)

"ranges": [
  "NULL < my_col < f",
  "f < my_col"
]

But this was not correct because the rows with values "foo" 
and "fee" would not belong to any of those ranges. However, the
predicate "my_col != 'f' AND my_col != 'h'" would translate
to 

"ranges": [
  "NULL < my_col"
]

because get_mm_leaf() changes from "<" to "<=" for partial
keyparts. This CS changes the range optimizer implementation 
for NOT IN to behave like a conjunction of NOT EQUAL: it 
replaces "<" with "<=" for all but the first range when the
keypart is partial.

sql/opt_range.cc

@@ -5345,6 +5345,34 @@ static SEL_TREE *get_func_mm_tree(RANGE_OPT_PARAM *param, Item_func *cond_func,
               {
                 new_interval->min_value= last_val->max_value;
                 new_interval->min_flag= NEAR_MIN;
+
+                /*
+                  If the interval is over a partial keypart, the
+                  interval must be "c_{i-1} <= X < c_i" instead of
+                  "c_{i-1} < X < c_i". Reason:
+
+                  Consider a table with a column "my_col VARCHAR(3)",
+                  and an index with definition
+                  "INDEX my_idx my_col(1)". If the table contains rows
+                  with my_col values "f" and "foo", the index will not
+                  distinguish the two rows.
+
+                  Note that tree_or() below will effectively merge
+                  this range with the range created for c_{i-1} and
+                  we'll eventually end up with only one range:
+                  "NULL < X".
+
+                  Partitioning indexes are never partial.
+                */
+                if (param->using_real_indexes)
+                {
+                  const KEY key=
+                    param->table->key_info[param->real_keynr[idx]];
+                  const KEY_PART_INFO *kpi= key.key_part + new_interval->part;
+
+                  if (kpi->key_part_flag & HA_PART_KEY_SEG)
+                    new_interval->min_flag= 0;
+                }
               }
             }
             /* 
@@ -5827,6 +5855,7 @@ get_mm_leaf(RANGE_OPT_PARAM *param, COND *conf_func, Field *field,
 
   if (key_part->image_type == Field::itMBR)
   {
+    // @todo: use is_spatial_operator() instead?
     switch (type) {
     case Item_func::SP_EQUALS_FUNC:
     case Item_func::SP_DISJOINT_FUNC: