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 (
    406193, 451309, 446162, 438117, 439044, 
    406083, 415033, 460158, 422354, 409660, 
    453640, 424754, 410340, 417422, 422439, 
    422004, 421990, 446415, 436834, 440447, 
    410009, 439533, 411516, 442635
  ) 
  AND cscart_product_descriptions.lang_code = 'zh'

Query time 0.00319

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 (406193,451309,446162,438117,439044,406083,415033,460158,422354,409660,453640,424754,410340,417422,422439,422004,421990,446415,436834,440447,410009,439533,411516,442635) and cscart_product_descriptions.lang_code = 'zh'"
        }
      }
    ]
  }
}