SELECT 
  category_id, 
  parent_id 
FROM 
  categories 
WHERE 
  parent_id IN(
    6781, 6782, 6767, 6737, 41, 6775, 6791, 
    6783, 6777, 6792, 40, 6761, 6768, 180, 
    61, 6784, 6776, 6785, 6789, 102, 6740, 
    6794, 6534, 6787, 6741, 6786, 6771, 
    6788, 6790, 6778, 6772, 42, 44, 101, 
    103, 80, 39, 12260
  )

Query time 0.00069

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "15.27"
    },
    "table": {
      "table_name": "categories",
      "access_type": "range",
      "possible_keys": [
        "parent"
      ],
      "key": "parent",
      "used_key_parts": [
        "parent_id"
      ],
      "key_length": "3",
      "rows_examined_per_scan": 73,
      "rows_produced_per_join": 73,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "7.97",
        "eval_cost": "7.30",
        "prefix_cost": "15.27",
        "data_read_per_join": "191K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`goimagine`.`categories`.`parent_id` in (6781,6782,6767,6737,41,6775,6791,6783,6777,6792,40,6761,6768,180,61,6784,6776,6785,6789,102,6740,6794,6534,6787,6741,6786,6771,6788,6790,6778,6772,42,44,101,103,80,39,12260))"
    }
  }
}