gistfile1.txt

    /*
      Conditions below:
       (1) - range analysis is used for estimating condition selectivity
       (2) - This is a unique key, and we have conditions for all its
             user-defined key parts.
       (3) - The table uses extended keys, this key covers all components,
             and we have conditions for all key parts.
    */
    if (!(cur->min_key_flag & ~NULL_RANGE) && !cur->max_key_flag &&
        (!key_info ||   // (1)
         ((uint)key_tree->part+1 == key_info->user_defined_key_parts && // (2)
          key_info->flags & HA_NOSAME) ||                               // (2)
         ((key_info->flags & HA_EXT_NOSAME) &&                 // (3)
          (uint)key_tree->part+1 == key_info->ext_key_parts)  // (3)
        ) &&
        range->start_key.length == range->end_key.length &&
        !memcmp(seq->param->min_key,seq->param->max_key,range->start_key.length))
      range->range_flag= UNIQUE_RANGE | (cur->min_key_flag & NULL_RANGE);