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 (
    46555, 46157, 4918, 46160, 46257, 27094, 
    1762, 47621, 48786, 46155, 48848, 46159, 
    46156, 48560, 46158, 49290, 4061, 4059, 
    48788, 4058, 48040, 43477, 4060, 48039, 
    4063, 49001, 4065, 48042, 48789, 49397, 
    4066, 48785
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00816

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 (46555,46157,4918,46160,46257,27094,1762,47621,48786,46155,48848,46159,46156,48560,46158,49290,4061,4059,48788,4058,48040,43477,4060,48039,4063,49001,4065,48042,48789,49397,4066,48785) and cscart_product_descriptions.lang_code = 'en'"
        }
      }
    ]
  }
}