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 (
    6368, 3519, 15322, 6274, 48559, 30368, 
    48251, 40381, 47828, 46583, 48557, 
    1945, 48244, 22263, 48503, 2859, 35177, 
    44946, 44943, 1977, 3578, 44944, 27356, 
    35167, 35165, 35174, 35176, 35173, 
    35170, 2291, 35172, 35171
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.00953

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 (6368,3519,15322,6274,48559,30368,48251,40381,47828,46583,48557,1945,48244,22263,48503,2859,35177,44946,44943,1977,3578,44944,27356,35167,35165,35174,35176,35173,35170,2291,35172,35171) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}