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 (
    426562, 446627, 409567, 403223, 456812, 
    416073, 444305, 414771, 405344, 428114, 
    460638, 435197, 412021, 450932, 405246, 
    430164, 444428, 428029, 441949, 460434, 
    433652, 426548, 416330, 447518
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00063

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 (426562,446627,409567,403223,456812,416073,444305,414771,405344,428114,460638,435197,412021,450932,405246,430164,444428,428029,441949,460434,433652,426548,416330,447518) and cscart_product_descriptions.lang_code = 'en'"
        }
      }
    ]
  }
}