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 (
    2321, 383, 2415, 6609, 144, 33306, 1120, 
    19567, 5198, 4020, 4239, 20665, 2564, 
    2506, 4702, 15454, 45505, 134, 1438, 
    32325, 6054, 3788, 38145, 2014, 6212, 
    4459, 1754, 2280, 2283, 38137, 33178, 
    4266
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.00295

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 (2321,383,2415,6609,144,33306,1120,19567,5198,4020,4239,20665,2564,2506,4702,15454,45505,134,1438,32325,6054,3788,38145,2014,6212,4459,1754,2280,2283,38137,33178,4266) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}