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 (
    48839, 630, 41341, 41340, 47922, 47921, 
    41343, 47896, 47924, 47923, 41339, 
    35730, 35731, 631, 2085, 4367, 35729, 
    5455, 637, 5581, 5577, 31872, 35859, 
    5461, 5958, 5476, 189, 4465, 4362, 33606, 
    5959, 47895
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.00225

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 (48839,630,41341,41340,47922,47921,41343,47896,47924,47923,41339,35730,35731,631,2085,4367,35729,5455,637,5581,5577,31872,35859,5461,5958,5476,189,4465,4362,33606,5959,47895) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}