Sandbox

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 (200) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00049

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_product_descriptions",
          "access_type": "const",
          "possible_keys": ["PRIMARY", "product_id"],
          "key": "PRIMARY",
          "key_length": "9",
          "used_key_parts": ["product_id", "lang_code"],
          "ref": ["const", "const"],
          "rows": 1,
          "filtered": 100
        }
      }
    ]
  }
}

Result

product_id	short_description	full_description	unit_name
200		<p><span style="font-size: small;">Список треков</span></p><p><span style="font-size: small;">1. Ding Dong! Merrily on High </span></p><p><span style="font-size: small;">2. The Colours of Christmas </span></p><p><span style="font-size: small;">3. In Dulci Jubilo </span></p><p><span style="font-size: small;">4. What is this lovely fragrance? </span></p><p><span style="font-size: small;">5. Away in a Manger </span></p><p><span style="font-size: small;">6. Hodie Christus natus est </span></p><p><span style="font-size: small;">7. Riu riu chiu </span></p><p><span style="font-size: small;">8. I wonder as I wander </span></p><p><span style="font-size: small;">9. Star Carol </span></p><p><span style="font-size: small;">10. Once in Royal David's City </span></p><p><span style="font-size: small;">11. Silent Night </span></p><p><span style="font-size: small;">12. In the bleak midwinter </span></p><p><span style="font-size: small;">13. Gabriel's Message </span></p><p><span style="font-size: small;">14. Fanfare - O come, all ye faithful </span></p><p><span style="font-size: small;">15. O Holy Night </span></p><p><span style="font-size: small;">16. A New Year Carol </span></p><p><span style="font-size: small;">17. Joy to the World </span></p><p><span style="font-size: small;">18. Sleigh Ride </span></p><p><span style="font-size: small;">19. Deck the Hall </span></p><p><span style="font-size: small;">20. The Christmas Song </span></p><p><span style="font-size: small;">21. The Twelve Days Of Christmas </span></p><p><span style="font-size: small;">22. Have yourself a merry little Christmas </span></p><p><span style="font-size: small;">23. Fanfare - Hark! the herald angels sing</span></p>