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 (
    422451, 420738, 440135, 427608, 430254, 
    422033, 405045, 420628, 445650, 409275, 
    417856, 421213, 459072, 434781, 459407, 
    447088, 436478, 422140, 428560, 456487, 
    411199, 403278, 449543, 407451
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00087

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.04252208,
    "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": 24,
          "cost": 0.04252208,
          "filtered": 100,
          "attached_condition": "cscart_product_descriptions.product_id in (422451,420738,440135,427608,430254,422033,405045,420628,445650,409275,417856,421213,459072,434781,459407,447088,436478,422140,428560,456487,411199,403278,449543,407451) and cscart_product_descriptions.lang_code = 'en'"
        }
      }
    ]
  }
}