SELECT 
  category_id, 
  parent_id 
FROM 
  categories 
WHERE 
  parent_id IN(
    6159, 6157, 6158, 5775, 5776, 21321, 
    5769, 5771, 5739, 5741, 5770, 5738, 
    5773, 5778, 5777, 5774, 7989, 5782, 
    5781, 5780, 5779, 19302
  )

Query time 0.00066

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "5.85"
    },
    "table": {
      "table_name": "categories",
      "access_type": "range",
      "possible_keys": [
        "parent"
      ],
      "key": "parent",
      "used_key_parts": [
        "parent_id"
      ],
      "key_length": "3",
      "rows_examined_per_scan": 26,
      "rows_produced_per_join": 26,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "3.25",
        "eval_cost": "2.60",
        "prefix_cost": "5.85",
        "data_read_per_join": "68K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`goimagine`.`categories`.`parent_id` in (6159,6157,6158,5775,5776,21321,5769,5771,5739,5741,5770,5738,5773,5778,5777,5774,7989,5782,5781,5780,5779,19302))"
    }
  }
}