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 (
    35687, 42166, 44760, 4918, 48828, 43668, 
    44874, 27094, 43669, 43667, 43664, 
    792, 37712, 43671, 32686, 40536, 47181, 
    47178, 42189, 41364, 990, 40384, 44938, 
    48565, 47891, 45294, 35911, 44936, 
    44934, 40385, 24711, 36659
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.02789

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 (35687,42166,44760,4918,48828,43668,44874,27094,43669,43667,43664,792,37712,43671,32686,40536,47181,47178,42189,41364,990,40384,44938,48565,47891,45294,35911,44936,44934,40385,24711,36659) and cscart_product_descriptions.lang_code = 'en'"
        }
      }
    ]
  }
}