SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    7857, 7997, 8049, 7946, 8090, 8156, 7976, 
    8031, 7990, 8015, 7959, 8064, 7895, 
    8072, 8163, 8132, 8146, 7858, 7947, 
    7977, 8032, 7998, 8091, 8065, 8157, 
    8147, 7859, 7978, 7999, 8092, 8033, 
    7860, 7979, 8093, 8034, 7980, 7861, 
    8094, 7862, 7981, 7863, 7864, 7865, 
    7866, 7867, 7868, 7869, 7870, 7871, 
    7872, 7873, 7874, 7875, 7876, 7877, 
    7878, 7879, 7880, 7881, 7882, 7883, 
    8104, 8050, 8051
  )

Query time 0.00093

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "34.67"
    },
    "table": {
      "table_name": "cscart_categories",
      "access_type": "range",
      "possible_keys": [
        "parent"
      ],
      "key": "parent",
      "used_key_parts": [
        "parent_id"
      ],
      "key_length": "3",
      "rows_examined_per_scan": 84,
      "rows_produced_per_join": 84,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "17.87",
        "eval_cost": "16.80",
        "prefix_cost": "34.67",
        "data_read_per_join": "498K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`webmarco`.`cscart_categories`.`parent_id` in (7857,7997,8049,7946,8090,8156,7976,8031,7990,8015,7959,8064,7895,8072,8163,8132,8146,7858,7947,7977,8032,7998,8091,8065,8157,8147,7859,7978,7999,8092,8033,7860,7979,8093,8034,7980,7861,8094,7862,7981,7863,7864,7865,7866,7867,7868,7869,7870,7871,7872,7873,7874,7875,7876,7877,7878,7879,7880,7881,7882,7883,8104,8050,8051))"
    }
  }
}