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 (
    6552, 6553, 1784, 31626, 83, 33720, 46749, 
    729, 6545, 81, 18748, 2254, 35187, 227, 
    6097, 33697, 2258, 1532, 6100, 40760, 
    43797, 332, 992, 1838, 1056, 5730, 141, 
    79, 2460, 5723, 5998, 5277
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.00886

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 (6552,6553,1784,31626,83,33720,46749,729,6545,81,18748,2254,35187,227,6097,33697,2258,1532,6100,40760,43797,332,992,1838,1056,5730,141,79,2460,5723,5998,5277) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}