SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.short_description, 
  IF(
    cscart_product_descriptions.short_description = '' 
    OR cscart_product_descriptions.short_description IS NULL, 
    cscart_product_descriptions.full_description, 
    ''
  ) AS full_description, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    425, 426, 427, 428, 429, 430, 431, 367, 
    402, 403, 404, 405, 406, 407, 408, 409, 
    410, 411, 412, 413, 414, 415, 416
  ) 
  AND cscart_product_descriptions.lang_code = 'de'

Query time 0.00036

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.04078329,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_product_descriptions",
          "access_type": "range",
          "possible_keys": ["PRIMARY", "product_id"],
          "key": "PRIMARY",
          "key_length": "9",
          "used_key_parts": ["product_id", "lang_code"],
          "loops": 1,
          "rows": 23,
          "cost": 0.04078329,
          "filtered": 100,
          "attached_condition": "cscart_product_descriptions.product_id in (425,426,427,428,429,430,431,367,402,403,404,405,406,407,408,409,410,411,412,413,414,415,416) and cscart_product_descriptions.lang_code = 'de'"
        }
      }
    ]
  }
}