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, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    13860, 13876, 13879, 13896, 13895, 13899, 
    13861, 13857, 13859, 13858, 13897, 
    13866, 13894, 13873, 13889, 13885, 
    13884, 13892, 13891, 13890, 13893
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00032

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.03730571,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_product_descriptions",
          "access_type": "range",
          "possible_keys": ["PRIMARY", "product_id"],
          "key": "PRIMARY",
          "key_length": "9",
          "used_key_parts": ["product_id", "lang_code"],
          "loops": 1,
          "rows": 21,
          "cost": 0.03730571,
          "filtered": 100,
          "attached_condition": "cscart_product_descriptions.product_id in (13860,13876,13879,13896,13895,13899,13861,13857,13859,13858,13897,13866,13894,13873,13889,13885,13884,13892,13891,13890,13893) and cscart_product_descriptions.lang_code = 'en'"
        }
      }
    ]
  }
}