SELECT 
  pfv.feature_id, 
  pfv.product_id, 
  pfv.variant_id, 
  fv.position, 
  fvd.variant 
FROM 
  cscart_product_features_values AS pfv 
  INNER JOIN cscart_product_feature_variants AS fv ON pfv.feature_id = fv.feature_id 
  AND pfv.variant_id = fv.variant_id 
  INNER JOIN cscart_product_feature_variant_descriptions AS fvd ON pfv.variant_id = fvd.variant_id 
  AND fvd.lang_code = 'en' 
WHERE 
  pfv.feature_id IN (601) 
  AND pfv.product_id IN (
    13439, 13440, 13441, 13442, 13443, 13444, 
    13445, 13446, 13447, 13448, 13449, 
    13450, 13451
  ) 
  AND pfv.lang_code = 'en'

Query time 0.00047

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.03493145,
    "nested_loop": [
      {
        "table": {
          "table_name": "fv",
          "access_type": "ref",
          "possible_keys": ["PRIMARY", "feature_id"],
          "key": "feature_id",
          "key_length": "3",
          "used_key_parts": ["feature_id"],
          "ref": ["const"],
          "loops": 1,
          "rows": 13,
          "cost": 0.01783744,
          "filtered": 100
        }
      },
      {
        "table": {
          "table_name": "pfv",
          "access_type": "ref",
          "possible_keys": [
            "PRIMARY",
            "fl",
            "variant_id",
            "lang_code",
            "product_id",
            "fpl",
            "idx_product_feature_variant_id"
          ],
          "key": "variant_id",
          "key_length": "6",
          "used_key_parts": ["variant_id", "feature_id"],
          "ref": ["u508912950_dev_2025.fv.variant_id", "const"],
          "loops": 13,
          "rows": 2,
          "cost": 0.01538037,
          "filtered": 2.844639063,
          "attached_condition": "pfv.product_id in (13439,13440,13441,13442,13443,13444,13445,13446,13447,13448,13449,13450,13451) and pfv.lang_code = 'en'",
          "using_index": true
        }
      },
      {
        "table": {
          "table_name": "fvd",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "9",
          "used_key_parts": ["variant_id", "lang_code"],
          "ref": ["u508912950_dev_2025.fv.variant_id", "const"],
          "loops": 1,
          "rows": 1,
          "cost": 0.00171364,
          "filtered": 100,
          "attached_condition": "fvd.lang_code = 'en'"
        }
      }
    ]
  }
}