Function add_key_field

sql/sql_select.cc:6789–6937

*/

static void
add_key_field(JOIN *join,
              KEY_FIELD **key_fields,uint and_level, Item_bool_func *cond,
              Field *field, bool eq_func, Item **value, uint num_values,
              table_map usable_tables, SARGABLE_PARAM **sargables,
              uint row_col_no= 0)
{
  uint optimize= 0;  
  if (eq_func &&
      ((join->is_allowed_hash_join_access(field->table) &&
        field->hash_join_is_possible() && 
        !(field->table->pos_in_table_list->is_materialized_derived() &&
          field->table->is_created())) ||
       (field->table->pos_in_table_list->is_materialized_derived() &&
        !field->table->is_created() && !(field->flags & BLOB_FLAG))))
  {
    optimize= KEY_OPTIMIZE_EQ;
  }   
  else if (!(field->flags & PART_KEY_FLAG))
  {
    // Don't remove column IS NULL on a LEFT JOIN table
    if (eq_func && (*value)->type() == Item::NULL_ITEM &&
        field->table->maybe_null && !field->null_ptr)
    {
      optimize= KEY_OPTIMIZE_EXISTS;
      DBUG_ASSERT(num_values == 1);
    }
  }
  if (optimize != KEY_OPTIMIZE_EXISTS)
  {
    table_map used_tables=0;
    bool optimizable=0;
    for (uint i=0; i<num_values; i++)
    {
      Item *curr_val; 
      if (row_col_no && value[i]->real_item()->type() == Item::ROW_ITEM)
      {
        Item_row *value_tuple= (Item_row *) (value[i]->real_item());
        curr_val= value_tuple->element_index(row_col_no - 1);
      }
      else
        curr_val= value[i];
      table_map value_used_tables= curr_val->used_tables();
      used_tables|= value_used_tables;
      if (!(value_used_tables & (field->table->map | RAND_TABLE_BIT)))
        optimizable=1;
    }
    if (!optimizable)
      return;
    if (!(usable_tables & field->table->map))
    {
      if (!eq_func || (*value)->type() != Item::NULL_ITEM ||
          !field->table->maybe_null || field->null_ptr)
	return;					// Can't use left join optimize
      optimize= KEY_OPTIMIZE_EXISTS;
    }
    else
    {