SELECT 
  category_id, 
  parent_id 
FROM 
  categories 
WHERE 
  parent_id IN(
    6817, 18879, 18881, 18878, 18880, 6365, 
    10333, 7712, 18857, 18877, 10335, 8443, 
    20143, 13358, 10812, 9321, 20955, 13357, 
    10334, 8499, 6866, 19803, 13628, 7905, 
    13359, 6358, 16173, 7714, 19514, 20611, 
    10336, 8695, 10409, 10161, 13356, 8031, 
    19509, 20302, 7713, 6483, 8489, 6247, 
    8488, 7265, 6368, 10482, 6369, 18886, 
    8694, 11350, 14094, 19515, 15466, 10853, 
    15094, 7695, 10163, 13321, 6366, 7266, 
    7221, 9148, 6370, 8498, 7405, 7710, 
    5843, 13579
  )

Query time 0.00214

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "32.51"
    },
    "table": {
      "table_name": "categories",
      "access_type": "range",
      "possible_keys": [
        "parent"
      ],
      "key": "parent",
      "used_key_parts": [
        "parent_id"
      ],
      "key_length": "3",
      "rows_examined_per_scan": 159,
      "rows_produced_per_join": 159,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "16.61",
        "eval_cost": "15.90",
        "prefix_cost": "32.51",
        "data_read_per_join": "416K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`goimagine`.`categories`.`parent_id` in (6817,18879,18881,18878,18880,6365,10333,7712,18857,18877,10335,8443,20143,13358,10812,9321,20955,13357,10334,8499,6866,19803,13628,7905,13359,6358,16173,7714,19514,20611,10336,8695,10409,10161,13356,8031,19509,20302,7713,6483,8489,6247,8488,7265,6368,10482,6369,18886,8694,11350,14094,19515,15466,10853,15094,7695,10163,13321,6366,7266,7221,9148,6370,8498,7405,7710,5843,13579))"
    }
  }
}