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 (
    502, 27002, 46548, 23017, 26889, 44858, 
    26897, 23047, 26876, 40441, 5994, 4512, 
    42111, 26893, 26878, 26888, 26885, 
    26875, 37095, 26881, 26879, 26884, 
    26883, 34676, 40439, 34673, 1718, 31629, 
    37314, 5781, 41205, 40434
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.00493

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 (502,27002,46548,23017,26889,44858,26897,23047,26876,40441,5994,4512,42111,26893,26878,26888,26885,26875,37095,26881,26879,26884,26883,34676,40439,34673,1718,31629,37314,5781,41205,40434) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}