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 (
    412939, 435593, 457221, 431380, 432643, 
    430955, 425786, 433168, 420963, 435716, 
    436514, 419288, 424427, 460521, 414020, 
    414696, 431630, 420330, 439312, 427057, 
    405641, 426607, 407640, 409611
  ) 
  AND cscart_product_descriptions.lang_code = 'zh'

Query time 0.01126

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.04252208,
    "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": 24,
          "cost": 0.04252208,
          "filtered": 100,
          "attached_condition": "cscart_product_descriptions.product_id in (412939,435593,457221,431380,432643,430955,425786,433168,420963,435716,436514,419288,424427,460521,414020,414696,431630,420330,439312,427057,405641,426607,407640,409611) and cscart_product_descriptions.lang_code = 'zh'"
        }
      }
    ]
  }
}