SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    7846, 7852, 7907, 7961, 8042, 8107, 8310, 
    8319, 8164, 8189, 8271, 7915, 7885, 
    7969, 8055, 7900, 8128, 8314, 8327, 
    8166, 8202, 8284, 7892, 7952, 7988, 
    8073, 8103, 8133, 8332, 8343, 8173, 
    8208, 8291, 7995, 8086, 8142, 8348, 
    8158, 8211, 8180, 8009, 8148, 8224, 
    8014, 8186, 8251, 8022, 8259, 8265, 
    8096, 8303
  )

Query time 0.00063

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 (7846,7852,7907,7961,8042,8107,8310,8319,8164,8189,8271,7915,7885,7969,8055,7900,8128,8314,8327,8166,8202,8284,7892,7952,7988,8073,8103,8133,8332,8343,8173,8208,8291,7995,8086,8142,8348,8158,8211,8180,8009,8148,8224,8014,8186,8251,8022,8259,8265,8096,8303))"
    }
  }
}