SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    6834, 6913, 6984, 7068, 7262, 7327, 7580, 
    7658, 7733, 7779, 7828, 7904
  )

Query time 0.00058

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "5.82"
    },
    "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": 12,
      "rows_produced_per_join": 12,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "3.42",
        "eval_cost": "2.40",
        "prefix_cost": "5.82",
        "data_read_per_join": "71K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`webmarco`.`cscart_categories`.`parent_id` in (6834,6913,6984,7068,7262,7327,7580,7658,7733,7779,7828,7904))"
    }
  }
}