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 (
    439645, 401030, 435106, 401667, 431036, 
    442622, 435820, 452529, 426624, 403050, 
    452048, 407841, 405943, 459502, 431667, 
    420500, 433248, 407007, 424261, 442071, 
    411571, 430068, 446914, 420739, 441207, 
    438933, 436348, 447332, 442119, 424436, 
    409550, 447602
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00394

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.0564324,
    "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": 32,
          "cost": 0.0564324,
          "filtered": 100,
          "attached_condition": "cscart_product_descriptions.product_id in (439645,401030,435106,401667,431036,442622,435820,452529,426624,403050,452048,407841,405943,459502,431667,420500,433248,407007,424261,442071,411571,430068,446914,420739,441207,438933,436348,447332,442119,424436,409550,447602) and cscart_product_descriptions.lang_code = 'en'"
        }
      }
    ]
  }
}