SELECT 
  cscart_product_feature_variant_descriptions.variant, 
  cscart_product_feature_variants.variant_id, 
  cscart_product_feature_variants.feature_id, 
  cscart_product_features_values.variant_id as selected, 
  cscart_product_features.feature_type 
FROM 
  cscart_product_feature_variants 
  LEFT JOIN cscart_product_feature_variant_descriptions ON cscart_product_feature_variant_descriptions.variant_id = cscart_product_feature_variants.variant_id 
  AND cscart_product_feature_variant_descriptions.lang_code = 'ja' 
  INNER JOIN cscart_product_features_values ON cscart_product_features_values.variant_id = cscart_product_feature_variants.variant_id 
  AND cscart_product_features_values.lang_code = 'ja' 
  AND cscart_product_features_values.product_id = 248 
  LEFT JOIN cscart_product_features ON cscart_product_features.feature_id = cscart_product_feature_variants.feature_id 
WHERE 
  1 
  AND cscart_product_feature_variants.feature_id IN (
    21, 23, 29, 28, 25, 26, 27, 35, 36, 31, 32, 
    45, 44, 43, 42
  ) 
GROUP BY 
  cscart_product_feature_variants.variant_id 
ORDER BY 
  cscart_product_feature_variants.position, 
  cscart_product_feature_variant_descriptions.variant

Query time 0.00007

JSON explain

{
  "query_block": {
    "select_id": 1,
    "filesort": {
      "sort_key": "cscart_product_feature_variants.position, cscart_product_feature_variant_descriptions.variant",
      "temporary_table": {
        "table": {
          "table_name": "cscart_product_features_values",
          "access_type": "ref",
          "possible_keys": [
            "variant_id",
            "lang_code",
            "product_id",
            "idx_product_feature_variant_id"
          ],
          "key": "idx_product_feature_variant_id",
          "key_length": "3",
          "used_key_parts": ["product_id"],
          "ref": ["const"],
          "rows": 62,
          "filtered": 71.13490295,
          "attached_condition": "cscart_product_features_values.product_id <=> 248 and cscart_product_features_values.lang_code = 'ja'",
          "using_index": true
        },
        "table": {
          "table_name": "cscart_product_feature_variants",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY", "feature_id"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["variant_id"],
          "ref": ["smscrm_edev.cscart_product_features_values.variant_id"],
          "rowid_filter": {
            "range": {
              "key": "feature_id",
              "used_key_parts": ["feature_id"]
            },
            "rows": 39,
            "selectivity_pct": 24.6835443
          },
          "rows": 1,
          "filtered": 24.68354416,
          "attached_condition": "cscart_product_feature_variants.feature_id in (21,23,29,28,25,26,27,35,36,31,32,45,44,43,42)"
        },
        "table": {
          "table_name": "cscart_product_features",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["feature_id"],
          "ref": ["smscrm_edev.cscart_product_feature_variants.feature_id"],
          "rows": 1,
          "filtered": 100
        },
        "table": {
          "table_name": "cscart_product_feature_variant_descriptions",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "9",
          "used_key_parts": ["variant_id", "lang_code"],
          "ref": ["smscrm_edev.cscart_product_features_values.variant_id", "const"],
          "rows": 1,
          "filtered": 100,
          "attached_condition": "trigcond(cscart_product_feature_variant_descriptions.lang_code = 'ja')"
        }
      }
    }
  }
}