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 (
    439522, 420223, 402063, 434025, 453641, 
    407875, 450825, 427907, 427353, 431455, 
    406944, 424119, 412948, 438098, 417337, 
    403309, 429951, 411429, 443819, 402148, 
    438958, 423821, 449843, 410922
  ) 
  AND cscart_product_descriptions.lang_code = 'ar'

Query time 0.00086

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 (439522,420223,402063,434025,453641,407875,450825,427907,427353,431455,406944,424119,412948,438098,417337,403309,429951,411429,443819,402148,438958,423821,449843,410922) and cscart_product_descriptions.lang_code = 'ar'"
        }
      }
    ]
  }
}