The pilot patch for mwl#253.

sql/field.h

@@ -220,7 +220,23 @@ public:
    */
   bool is_created_from_null_item;
 
-  bool is_stat_field; /* TRUE in Field objects created for column min/max values */
+  /* TRUE in Field objects created for column min/max values */
+  bool is_stat_field; 
+
+  /* 
+    Selectivity of the range condition over this field.
+    When calculating this selectivity a range predicate
+    is taken into account only if:
+    - it is extracted from the WHERE clause
+    - it depends only on the table the field belongs to 
+  */
+  double cond_selectivity;
+
+  /* 
+    The next field in the class of equal fields at the top AND level
+    of the WHERE clause
+  */ 
+  Field *next_equal_field;
 
   /*
     This structure is used for statistical data on the column
@@ -703,6 +719,11 @@ public:
   virtual bool hash_join_is_possible() { return TRUE; }
   virtual bool eq_cmp_as_binary() { return TRUE; }
 
+  virtual double middle_point_pos(Field *min, Field *max)
+  {
+    return (double) 1.0; 
+  }
+
   friend int cre_myisam(char * name, register TABLE *form, uint options,
 			ulonglong auto_increment_value);
   friend class Copy_field;
@@ -821,6 +842,7 @@ public:
   bool get_int(CHARSET_INFO *cs, const char *from, uint len, 
                longlong *rnd, ulonglong unsigned_max, 
                longlong signed_min, longlong signed_max);
+  double middle_point_pos(Field *min, Field *max);
 };
 
 
@@ -866,6 +888,8 @@ public:
   virtual bool str_needs_quotes() { return TRUE; }
   uint is_equal(Create_field *new_field);
   bool eq_cmp_as_binary() { return test(flags & BINARY_FLAG); }
+  virtual uint length_size() { return 0; }
+  double middle_point_pos(Field *min, Field *max);
 };
 
 /* base class for Field_string, Field_varstring and Field_blob */
@@ -1894,6 +1918,7 @@ public:
                        uint new_null_bit);
   uint is_equal(Create_field *new_field);
   void hash(ulong *nr, ulong *nr2);
+  uint length_size() { return length_bytes; }
 private:
   int do_save_field_metadata(uchar *first_byte);
 };