Function is_foreign_key_prefix

sql/sql_class.cc:215–274

*/

bool is_foreign_key_prefix(Key *a, Key *b)
{
  ha_key_alg a_alg= a->key_create_info.algorithm;
  ha_key_alg b_alg= b->key_create_info.algorithm;

  // The real algorithm in InnoDB will be BTREE if none was given by user.
  a_alg= a_alg == HA_KEY_ALG_UNDEF ? HA_KEY_ALG_BTREE : a_alg;
  b_alg= b_alg == HA_KEY_ALG_UNDEF ? HA_KEY_ALG_BTREE : b_alg;

  if (a_alg != b_alg)
    return false;

  /* Ensure that 'a' is the generated key */
  if (a->generated)
  {
    if (b->generated && a->columns.elements > b->columns.elements)
      swap_variables(Key*, a, b);               // Put shorter key in 'a'
  }
  else
  {
    if (!b->generated)
      return false;                             // No foreign key
    swap_variables(Key*, a, b);                 // Put generated key in 'a'
  }

  /* Test if 'a' is a prefix of 'b' */
  if (a->columns.elements > b->columns.elements)
    return false;                                // Can't be prefix

  List_iterator<Key_part_spec> col_it1(a->columns);
  List_iterator<Key_part_spec> col_it2(b->columns);
  const Key_part_spec *col1, *col2;

#ifdef ENABLE_WHEN_INNODB_CAN_HANDLE_SWAPED_FOREIGN_KEY_COLUMNS
  while ((col1= col_it1++))
  {
    bool found= 0;
    col_it2.rewind();
    while ((col2= col_it2++))
    {
      if (*col1 == *col2)
      {
        found= TRUE;
	break;
      }
    }
    if (!found)
      return false;                             // Error
  }
  return true;                                  // Is prefix
#else
  while ((col1= col_it1++))
  {
    col2= col_it2++;
    if (!(*col1 == *col2))
      return false;
  }
  return true;                                 // Is prefix