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 (
    630, 35833, 35804, 31966, 35859, 4465, 
    4362, 33625, 5578, 5579, 5478, 5580, 
    31887, 31891, 31894, 31893, 31895, 
    4361, 5479, 4366, 4360, 5485, 31889, 
    31886, 4358, 4464, 4466, 31897, 4359, 
    5481, 31896, 4357
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.00925

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 (630,35833,35804,31966,35859,4465,4362,33625,5578,5579,5478,5580,31887,31891,31894,31893,31895,4361,5479,4366,4360,5485,31889,31886,4358,4464,4466,31897,4359,5481,31896,4357) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}