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 (
    2921, 2932, 3774, 2926, 5411, 3781, 3789, 
    2917, 2906, 5424, 2910, 5421, 3786, 
    3773, 3776, 3771, 2899, 5408, 3788, 
    3787, 5407, 3785, 3784, 3778, 1732, 
    2904, 3770, 3777, 5418, 5416
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.01325

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": 30,
          "filtered": 100,
          "index_condition": "cscart_product_descriptions.product_id in (2921,2932,3774,2926,5411,3781,3789,2917,2906,5424,2910,5421,3786,3773,3776,3771,2899,5408,3788,3787,5407,3785,3784,3778,1732,2904,3770,3777,5418,5416) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}