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, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    402092, 403976, 408452, 428407, 451396, 
    417863, 404877, 460518, 418662, 425706, 
    403670, 447102, 447465, 418224, 454664, 
    413860, 446202, 446424, 416636, 436995, 
    424216, 416027, 453105, 414898, 420267, 
    412406, 425747, 441765, 406851, 447289, 
    403492, 409045, 411798, 455469, 403314, 
    459175, 412726, 446945, 419788, 441409, 
    421788, 429875, 408990, 457492, 402535, 
    424481, 421915, 427033
  ) 
  AND cscart_product_descriptions.lang_code = 'zh'

Query time 0.00126

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.08425304,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_product_descriptions",
          "access_type": "range",
          "possible_keys": ["PRIMARY", "product_id"],
          "key": "PRIMARY",
          "key_length": "9",
          "used_key_parts": ["product_id", "lang_code"],
          "loops": 1,
          "rows": 48,
          "cost": 0.08425304,
          "filtered": 100,
          "attached_condition": "cscart_product_descriptions.product_id in (402092,403976,408452,428407,451396,417863,404877,460518,418662,425706,403670,447102,447465,418224,454664,413860,446202,446424,416636,436995,424216,416027,453105,414898,420267,412406,425747,441765,406851,447289,403492,409045,411798,455469,403314,459175,412726,446945,419788,441409,421788,429875,408990,457492,402535,424481,421915,427033) and cscart_product_descriptions.lang_code = 'zh'"
        }
      }
    ]
  }
}