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 (
    47655, 27359, 34555, 31638, 33312, 31633, 
    5300, 5991, 5297, 1980, 31634, 31639, 
    3570, 3569, 31636, 1979, 1088, 17259, 
    398, 1981, 31637, 5278, 31635, 1580, 
    48980, 120, 37850, 1538, 48558, 15322, 
    6274, 40381
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.00448

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 (47655,27359,34555,31638,33312,31633,5300,5991,5297,1980,31634,31639,3570,3569,31636,1979,1088,17259,398,1981,31637,5278,31635,1580,48980,120,37850,1538,48558,15322,6274,40381) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}