SELECT 
  f.feature_id, 
  f.purpose, 
  p.product_id, 
  p.parent_product_id, 
  g.id, 
  g.code 
FROM 
  cscart_product_variation_group_features AS f 
  INNER JOIN cscart_product_variation_groups AS g ON f.group_id = g.id 
  INNER JOIN cscart_product_variation_group_products AS p ON f.group_id = p.group_id 
WHERE 
  p.product_id IN (
    66798, 66799, 66800, 66801, 66802, 66803, 
    66804, 66805, 66806, 66807, 66808, 
    66809, 66810, 66811, 66812, 66813, 
    66814, 66815, 66816, 66817, 66818, 
    66819, 66820, 66821, 66822, 66823, 
    66824, 66825, 66826, 66827, 66828, 
    66904, 66905
  )

Query time 0.00030

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "46.21"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "p",
          "access_type": "range",
          "possible_keys": [
            "PRIMARY",
            "idx_group_id"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "product_id"
          ],
          "key_length": "3",
          "rows_examined_per_scan": 33,
          "rows_produced_per_join": 33,
          "filtered": "100.00",
          "index_condition": "(`cscart_db`.`p`.`product_id` in (66798,66799,66800,66801,66802,66803,66804,66805,66806,66807,66808,66809,66810,66811,66812,66813,66814,66815,66816,66817,66818,66819,66820,66821,66822,66823,66824,66825,66826,66827,66828,66904,66905))",
          "cost_info": {
            "read_cost": "19.81",
            "eval_cost": "3.30",
            "prefix_cost": "23.11",
            "data_read_per_join": "528"
          },
          "used_columns": [
            "product_id",
            "parent_product_id",
            "group_id"
          ]
        }
      },
      {
        "table": {
          "table_name": "g",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "id"
          ],
          "key_length": "3",
          "ref": [
            "cscart_db.p.group_id"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 33,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "8.25",
            "eval_cost": "3.30",
            "prefix_cost": "34.66",
            "data_read_per_join": "12K"
          },
          "used_columns": [
            "id",
            "code"
          ]
        }
      },
      {
        "table": {
          "table_name": "f",
          "access_type": "ref",
          "possible_keys": [
            "idx_group_id"
          ],
          "key": "idx_group_id",
          "used_key_parts": [
            "group_id"
          ],
          "key_length": "3",
          "ref": [
            "cscart_db.p.group_id"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 33,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "8.25",
            "eval_cost": "3.30",
            "prefix_cost": "46.21",
            "data_read_per_join": "3K"
          },
          "used_columns": [
            "feature_id",
            "purpose",
            "group_id"
          ]
        }
      }
    ]
  }
}