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 (
    49186, 1997, 37290, 6482, 3668, 41384, 
    3190, 4191, 20598, 31871, 3748, 3195, 
    1992, 47274, 2152, 38147, 28171, 36758, 
    37288, 38102, 4294, 1847, 1999, 2009, 
    22466, 37287, 1472, 2464, 36301, 1996, 
    38157, 36271
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.02525

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 (49186,1997,37290,6482,3668,41384,3190,4191,20598,31871,3748,3195,1992,47274,2152,38147,28171,36758,37288,38102,4294,1847,1999,2009,22466,37287,1472,2464,36301,1996,38157,36271) and cscart_product_descriptions.lang_code = 'en'"
        }
      }
    ]
  }
}