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 (
    303, 304, 305, 328, 310, 311, 312, 313, 
    314, 315, 316, 317, 318, 319, 320, 321, 
    327, 291, 292, 307, 296, 297, 293, 294, 
    308, 302, 306, 309, 298, 299, 300, 301
  )

Query time 0.00030

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "g",
          "access_type": "system",
          "possible_keys": ["PRIMARY"],
          "rows": 1,
          "filtered": 100
        }
      },
      {
        "table": {
          "table_name": "f",
          "access_type": "ref",
          "possible_keys": ["idx_group_id"],
          "key": "idx_group_id",
          "key_length": "3",
          "used_key_parts": ["group_id"],
          "ref": ["const"],
          "rows": 2,
          "filtered": 100
        }
      },
      {
        "block-nl-join": {
          "table": {
            "table_name": "p",
            "access_type": "ALL",
            "possible_keys": ["PRIMARY", "idx_group_id"],
            "rows": 7,
            "filtered": 100,
            "attached_condition": "p.group_id = 10 and p.product_id in (303,304,305,328,310,311,312,313,314,315,316,317,318,319,320,321,327,291,292,307,296,297,293,294,308,302,306,309,298,299,300,301)"
          },
          "buffer_type": "flat",
          "buffer_size": "1Kb",
          "join_type": "BNL"
        }
      }
    ]
  }
}