SELECT 
  pf.feature_id, 
  pf.feature_style, 
  pf.position, 
  pf.purpose, 
  pf.display_on_catalog, 
  pfd.description, 
  pfd.internal_name, 
  pfd.prefix, 
  pfd.suffix, 
  (
    CASE WHEN pf.purpose = 'group_catalog_item' THEN 0 ELSE 1 END
  ) AS purpose_position 
FROM 
  cscart_product_features AS pf 
  INNER JOIN cscart_product_features_descriptions AS pfd ON pf.feature_id = pfd.feature_id 
  AND pfd.lang_code = 'en' 
WHERE 
  pf.feature_id IN (551) 
ORDER BY 
  purpose_position ASC, 
  pf.position ASC, 
  pf.feature_id ASC

Query time 0.00023

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "pf",
      "access_type": "const",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "3",
      "used_key_parts": ["feature_id"],
      "ref": ["const"],
      "rows": 1,
      "filtered": 100
    },
    "table": {
      "table_name": "pfd",
      "access_type": "const",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "9",
      "used_key_parts": ["feature_id", "lang_code"],
      "ref": ["const", "const"],
      "rows": 1,
      "filtered": 100
    }
  }
}