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 (
    26868, 46144, 44931, 6165, 28238, 26867, 
    46142, 46145, 44930, 46148, 6148, 47898, 
    46149, 41952, 46147, 47165, 47166, 
    47897, 41955, 47167, 47668, 46146, 
    43662, 41954, 47664, 47168, 47665, 
    49394, 41953, 47667, 16567, 41956
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.00454

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 (26868,46144,44931,6165,28238,26867,46142,46145,44930,46148,6148,47898,46149,41952,46147,47165,47166,47897,41955,47167,47668,46146,43662,41954,47664,47168,47665,49394,41953,47667,16567,41956) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}