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 (
    45574, 33714, 5595, 28135, 41356, 37890, 
    4885, 41373, 4190, 41126, 33292, 6174, 
    4303, 28145, 27289, 4308, 41369, 31941, 
    41107, 35223, 5766, 44556, 44483, 33279, 
    790, 41376, 1753, 31945, 4179, 1743, 
    40506, 31739
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00189

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 (45574,33714,5595,28135,41356,37890,4885,41373,4190,41126,33292,6174,4303,28145,27289,4308,41369,31941,41107,35223,5766,44556,44483,33279,790,41376,1753,31945,4179,1743,40506,31739) and cscart_product_descriptions.lang_code = 'en'"
        }
      }
    ]
  }
}