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 (
    47865, 47891, 47890, 47892, 47867, 47888, 
    47887, 47868, 48497, 47862, 47858, 
    47889, 47856, 47861, 47860, 47859, 
    47857, 47863, 47866, 48499, 48498, 
    48494, 48496, 48495
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00206

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": 24,
          "filtered": 100,
          "index_condition": "cscart_product_descriptions.product_id in (47865,47891,47890,47892,47867,47888,47887,47868,48497,47862,47858,47889,47856,47861,47860,47859,47857,47863,47866,48499,48498,48494,48496,48495) and cscart_product_descriptions.lang_code = 'en'"
        }
      }
    ]
  }
}