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 (
    4373, 36464, 5575, 976, 5636, 4379, 6476, 
    3995, 38561, 21746, 23481, 16847, 1051, 
    36474, 3224, 2653, 975, 5726, 41437, 
    16416, 28162, 5405, 1358, 3989, 6470, 
    38136, 32286, 4372, 285, 1166, 5414, 
    38551
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.00403

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 (4373,36464,5575,976,5636,4379,6476,3995,38561,21746,23481,16847,1051,36474,3224,2653,975,5726,41437,16416,28162,5405,1358,3989,6470,38136,32286,4372,285,1166,5414,38551) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}