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 (
    33725, 33723, 33724, 856, 34053, 857, 
    35734, 6468, 4269, 1750, 6545, 4271, 
    5769, 4272, 1751, 461, 4268, 4267, 5775, 
    41616, 5771, 41226, 5768, 33721, 1753, 
    35475, 48062, 40312, 47855, 35470, 
    35471, 50297
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.00319

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 (33725,33723,33724,856,34053,857,35734,6468,4269,1750,6545,4271,5769,4272,1751,461,4268,4267,5775,41616,5771,41226,5768,33721,1753,35475,48062,40312,47855,35470,35471,50297) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}