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 (
    5300, 3517, 5991, 3516, 33744, 5297, 
    1980, 1103, 65, 31634, 35782, 5784, 
    3518, 40445, 40442, 31631, 31639, 22172, 
    15462, 47024, 1278, 2289, 1102, 3871, 
    3570, 3569, 31636, 1104, 1979, 1088, 
    41293, 17259
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.00368

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 (5300,3517,5991,3516,33744,5297,1980,1103,65,31634,35782,5784,3518,40445,40442,31631,31639,22172,15462,47024,1278,2289,1102,3871,3570,3569,31636,1104,1979,1088,41293,17259) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}