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 (
    3587, 5549, 34671, 27863, 2964, 31640, 
    40440, 3586, 45507, 389, 1713, 44422, 
    2278, 3874, 2514, 2287, 5569, 46751, 
    6059, 48769, 31630, 6060, 4440, 18258, 
    14822, 18201, 2461, 31909, 31908, 2505, 
    4441, 6099
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.00301

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 (3587,5549,34671,27863,2964,31640,40440,3586,45507,389,1713,44422,2278,3874,2514,2287,5569,46751,6059,48769,31630,6060,4440,18258,14822,18201,2461,31909,31908,2505,4441,6099) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}