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 (
    3978, 3977, 49256, 36307, 4381, 1050, 
    3974, 2252, 33709, 3988, 36717, 43650, 
    36297, 2249, 40535, 33824, 353, 36295, 
    33721, 34678, 2260, 36300, 40532, 40527, 
    41230, 25159, 33713, 49309, 3979, 36293, 
    18710, 33835
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.01027

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 (3978,3977,49256,36307,4381,1050,3974,2252,33709,3988,36717,43650,36297,2249,40535,33824,353,36295,33721,34678,2260,36300,40532,40527,41230,25159,33713,49309,3979,36293,18710,33835) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}