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 (
    13944, 13909, 14031, 14025, 13924, 13921, 
    13857, 13859, 13858, 13897, 14030, 
    14029, 13866, 13908, 14021, 13894, 
    13969, 14019, 13951, 13873, 13974, 
    13989, 13930, 13938
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00036

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.04252208,
    "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": 24,
          "cost": 0.04252208,
          "filtered": 100,
          "attached_condition": "cscart_product_descriptions.product_id in (13944,13909,14031,14025,13924,13921,13857,13859,13858,13897,14030,14029,13866,13908,14021,13894,13969,14019,13951,13873,13974,13989,13930,13938) and cscart_product_descriptions.lang_code = 'en'"
        }
      }
    ]
  }
}