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 (
    13439, 13440, 13441, 13442, 13443, 13444, 
    13445, 13446, 13447, 13448, 13449, 
    13450, 13451, 13452, 13453, 13454, 
    13455, 13456, 13457, 13458, 13459, 
    13460, 13461, 13462
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00037

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 (13439,13440,13441,13442,13443,13444,13445,13446,13447,13448,13449,13450,13451,13452,13453,13454,13455,13456,13457,13458,13459,13460,13461,13462) and cscart_product_descriptions.lang_code = 'en'"
        }
      }
    ]
  }
}