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 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    4287, 41366, 35690, 42187, 794, 35475, 
    42170, 48851, 41381, 42182, 36522, 
    37292, 6481, 5599, 42185, 24715, 5592, 
    44940, 42168, 42186, 27078, 27076, 
    985, 45601, 37281, 41402, 42163, 5596, 
    42162, 42181, 44599, 41377
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00162

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_product_descriptions",
          "access_type": "range",
          "possible_keys": ["PRIMARY", "product_id"],
          "key": "PRIMARY",
          "key_length": "11",
          "used_key_parts": ["product_id", "lang_code"],
          "rows": 32,
          "filtered": 100,
          "index_condition": "cscart_product_descriptions.product_id in (4287,41366,35690,42187,794,35475,42170,48851,41381,42182,36522,37292,6481,5599,42185,24715,5592,44940,42168,42186,27078,27076,985,45601,37281,41402,42163,5596,42162,42181,44599,41377) and cscart_product_descriptions.lang_code = 'en'"
        }
      }
    ]
  }
}