cleanup: avoid Field::field_index

prefer x->field over table->field[x->field->field_index]

sql/item_subselect.cc

@@ -6186,7 +6186,7 @@ subselect_rowid_merge_engine::init(MY_BITMAP *non_null_key_parts,
         Check if the first and only indexed column contains NULL in the curent
         row, and add the row number to the corresponding key.
       */
-      if (tmp_table->field[merge_keys[i]->get_field_idx(0)]->is_null())
+      if (merge_keys[i]->get_field(0)->is_null())
         merge_keys[i]->set_null(cur_rownum);
       else
         merge_keys[i]->add_key(cur_rownum);

sql/item_subselect.h

@@ -1236,10 +1236,10 @@ class Ordered_key : public Sql_alloc
 
   uint get_column_count() { return key_column_count; }
   uint get_keyid() { return keyid; }
-  uint get_field_idx(uint i)
+  Field *get_field(uint i)
   {
     DBUG_ASSERT(i < key_column_count);
-    return key_columns[i]->field->field_index;
+    return key_columns[i]->field;
   }
   rownum_t get_min_null_row() { return min_null_row; }
   rownum_t get_max_null_row() { return max_null_row; }

sql/sql_load.cc

@@ -881,7 +881,7 @@ read_fixed_length(THD *thd, COPY_INFO &info, TABLE_LIST *table_list,
 
   while ((sql_field= (Item_field*) it++))
   {
-    if (table->field[sql_field->field->field_index] == table->next_number_field)
+    if (sql_field->field == table->next_number_field)
       auto_increment_field_not_null= true;
   }
 

sql/sql_statistics.cc

@@ -3591,7 +3591,7 @@ double get_column_avg_frequency(Field * field)
     return res;
   }
  
-  Column_statistics *col_stats= table->s->field[field->field_index]->read_stats;
+  Column_statistics *col_stats= field->read_stats;
 
   if (!col_stats)
     res= table->stat_records();
@@ -3629,7 +3629,7 @@ double get_column_range_cardinality(Field *field,
 {
   double res;
   TABLE *table= field->table;
-  Column_statistics *col_stats= table->field[field->field_index]->read_stats;
+  Column_statistics *col_stats= field->read_stats;
   double tab_records= table->stat_records();
 
   if (!col_stats)