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 (
    6648, 38552, 31907, 20804, 26467, 83, 
    4880, 5756, 33720, 24988, 47278, 3777, 
    729, 39612, 81, 18748, 31919, 788, 2437, 
    5629, 3174, 35187, 2254, 41420, 33697, 
    356, 2258, 934, 43797, 992, 332, 1532
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.00316

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 (6648,38552,31907,20804,26467,83,4880,5756,33720,24988,47278,3777,729,39612,81,18748,31919,788,2437,5629,3174,35187,2254,41420,33697,356,2258,934,43797,992,332,1532) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}