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 (
    48813, 45029, 46155, 47878, 47614, 48560, 
    40524, 48836, 44758, 49290, 40713, 
    45241, 41440, 3616, 43477, 2044, 43856, 
    47871, 48551, 49001, 47615, 47612, 
    47870, 48938, 41431, 35685, 41434, 
    41432, 48939, 2042, 48550, 321
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.00256

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 (48813,45029,46155,47878,47614,48560,40524,48836,44758,49290,40713,45241,41440,3616,43477,2044,43856,47871,48551,49001,47615,47612,47870,48938,41431,35685,41434,41432,48939,2042,48550,321) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}