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 (
    40436, 31910, 5992, 1535, 41429, 47184, 
    47600, 6093, 31912, 5782, 47012, 3580, 
    6354, 31965, 37098, 26892, 48998, 40450, 
    37092, 2154, 41291, 5785, 737, 26880, 
    35740, 33702, 1484, 37096, 37093, 386, 
    41279, 2292
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.01726

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 (40436,31910,5992,1535,41429,47184,47600,6093,31912,5782,47012,3580,6354,31965,37098,26892,48998,40450,37092,2154,41291,5785,737,26880,35740,33702,1484,37096,37093,386,41279,2292) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}