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 (
    13407, 13439, 13440, 13441, 13442, 13443, 
    13499, 13444, 13445, 13408, 13446, 
    13447, 13448, 13409, 13504, 13410, 
    13449, 13450, 13411, 13412, 13413, 
    13414, 13415, 13451
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00034

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 (13407,13439,13440,13441,13442,13443,13499,13444,13445,13408,13446,13447,13448,13409,13504,13410,13449,13450,13411,13412,13413,13414,13415,13451) and cscart_product_descriptions.lang_code = 'en'"
        }
      }
    ]
  }
}