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 (
    426562, 446627, 409567, 403223, 456812, 
    416073, 444305, 414771, 405344, 428114, 
    460638, 435197, 412021, 450932, 405246, 
    430164, 444428, 428029, 441949, 460434, 
    433652, 426548, 416330, 447518
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00063

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 (426562,446627,409567,403223,456812,416073,444305,414771,405344,428114,460638,435197,412021,450932,405246,430164,444428,428029,441949,460434,433652,426548,416330,447518) and cscart_product_descriptions.lang_code = 'en'"
        }
      }
    ]
  }
}

Result

product_id short_description full_description unit_name
403223 Lite Laptop 334 — high quality, tested and ready to ship. Generated sample data for CS-Cart import.
405246 Lite Router 205 — high quality, tested and ready to ship. Generated sample data for CS-Cart import.
405344 Lite Mixer 486 — high quality, tested and ready to ship. Generated sample data for CS-Cart import.
409567 Lite Laptop 263 — high quality, tested and ready to ship. Generated sample data for CS-Cart import.
412021 Lite Phone 696 — high quality, tested and ready to ship. Generated sample data for CS-Cart import.
414771 Lite Mixer 440 — high quality, tested and ready to ship. Generated sample data for CS-Cart import.
416073 Lite Laptop 594 — high quality, tested and ready to ship. Generated sample data for CS-Cart import.
416330 Lite Router 877 — high quality, tested and ready to ship. Generated sample data for CS-Cart import.
426548 Lite Router 699 — high quality, tested and ready to ship. Generated sample data for CS-Cart import.
426562 Lite Headphones 807 — high quality, tested and ready to ship. Generated sample data for CS-Cart import.
428029 Lite Router 331 — high quality, tested and ready to ship. Generated sample data for CS-Cart import.
428114 Lite Mixer 634 — high quality, tested and ready to ship. Generated sample data for CS-Cart import.
430164 Lite Router 255 — high quality, tested and ready to ship. Generated sample data for CS-Cart import.
433652 Lite Router 557 — high quality, tested and ready to ship. Generated sample data for CS-Cart import.
435197 Lite Phone 684 — high quality, tested and ready to ship. Generated sample data for CS-Cart import.
441949 Lite Router 362 — high quality, tested and ready to ship. Generated sample data for CS-Cart import.
444305 Lite Laptop 781 — high quality, tested and ready to ship. Generated sample data for CS-Cart import.
444428 Lite Router 302 — high quality, tested and ready to ship. Generated sample data for CS-Cart import.
446627 Lite Laptop 257 — high quality, tested and ready to ship. Generated sample data for CS-Cart import.
447518 Lite Shirt 114 — high quality, tested and ready to ship. Generated sample data for CS-Cart import.
450932 Lite Router 128 — high quality, tested and ready to ship. Generated sample data for CS-Cart import.
456812 Lite Laptop 409 — high quality, tested and ready to ship. Generated sample data for CS-Cart import.
460434 Lite Router 448 — high quality, tested and ready to ship. Generated sample data for CS-Cart import.
460638 Lite Mixer 946 — high quality, tested and ready to ship. Generated sample data for CS-Cart import.