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 (
    264945, 264756, 264208, 264156, 264888, 
    264851, 264304, 264940, 264893, 264950, 
    264824, 264955, 264226, 263720, 264931
  )

Query time 0.00102

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "64.54"
    },
    "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": 15,
          "rows_produced_per_join": 15,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "18.03",
            "eval_cost": "3.00",
            "prefix_cost": "21.03",
            "data_read_per_join": "240"
          },
          "used_columns": [
            "product_id",
            "parent_product_id",
            "group_id"
          ],
          "attached_condition": "(`webmarco`.`p`.`product_id` in (264945,264756,264208,264156,264888,264851,264304,264940,264893,264950,264824,264955,264226,263720,264931))"
        }
      },
      {
        "table": {
          "table_name": "g",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "id"
          ],
          "key_length": "3",
          "ref": [
            "webmarco.p.group_id"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 15,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "15.00",
            "eval_cost": "3.00",
            "prefix_cost": "39.03",
            "data_read_per_join": "5K"
          },
          "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": [
            "webmarco.p.group_id"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 21,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "21.26",
            "eval_cost": "4.25",
            "prefix_cost": "64.54",
            "data_read_per_join": "2K"
          },
          "used_columns": [
            "feature_id",
            "purpose",
            "group_id"
          ]
        }
      }
    ]
  }
}