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 (
    21063, 1056, 1711, 40811, 5772, 14982, 
    4939, 1748, 5758, 40802, 5757, 43827, 
    47564, 49287, 49289, 48472, 48475
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.00345

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": 17,
          "filtered": 100,
          "index_condition": "cscart_product_descriptions.product_id in (21063,1056,1711,40811,5772,14982,4939,1748,5758,40802,5757,43827,47564,49287,49289,48472,48475) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}