SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    7669, 6556, 6653, 6676, 6926, 7804, 7071, 
    7724, 6578, 6869, 6724, 6957, 7674, 
    7219, 7814, 6603, 7729, 7297, 6754, 
    6986, 9056, 7820, 6617, 6787, 7014, 
    7736, 7826, 7339, 6832, 7278, 7782, 
    7832, 7351, 7789, 7375, 7544, 7546, 
    7549, 7550, 7553, 7557, 7560, 7564, 
    7567, 7573, 7576, 7583, 7589, 7594, 
    7600, 7608, 7612, 7643, 7774, 7791, 
    7796
  )

Query time 0.00071

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "32.27"
    },
    "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": 78,
      "rows_produced_per_join": 78,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "16.67",
        "eval_cost": "15.60",
        "prefix_cost": "32.27",
        "data_read_per_join": "462K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`webmarco`.`cscart_categories`.`parent_id` in (7669,6556,6653,6676,6926,7804,7071,7724,6578,6869,6724,6957,7674,7219,7814,6603,7729,7297,6754,6986,9056,7820,6617,6787,7014,7736,7826,7339,6832,7278,7782,7832,7351,7789,7375,7544,7546,7549,7550,7553,7557,7560,7564,7567,7573,7576,7583,7589,7594,7600,7608,7612,7643,7774,7791,7796))"
    }
  }
}