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 (
    13916, 13919, 13929, 13932, 13902, 13931, 
    13939, 13913, 13909, 13924, 13921, 
    13908, 13930, 13938, 13917, 13926, 
    13905, 13906, 13936, 13904, 13933, 
    13912, 13928
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00029

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 (13916,13919,13929,13932,13902,13931,13939,13913,13909,13924,13921,13908,13930,13938,13917,13926,13905,13906,13936,13904,13933,13912,13928) and cscart_product_descriptions.lang_code = 'en'"
        }
      }
    ]
  }
}