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 (
    90712, 90718, 90586, 90587, 90730, 90731, 
    90616, 90617, 90622, 90623, 90724, 
    90726, 90716, 90722, 90592, 90593, 
    92534, 89243, 89244, 89253, 89254, 
    90588, 90590, 90657, 90642, 92533, 
    90664, 90665, 90670, 90671
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00041

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "13.52"
    },
    "table": {
      "table_name": "cscart_product_descriptions",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY",
        "product_id"
      ],
      "key": "PRIMARY",
      "used_key_parts": [
        "product_id",
        "lang_code"
      ],
      "key_length": "9",
      "rows_examined_per_scan": 30,
      "rows_produced_per_join": 30,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "10.52",
        "eval_cost": "3.00",
        "prefix_cost": "13.52",
        "data_read_per_join": "114K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description"
      ],
      "attached_condition": "((`nuie_scalesta_net`.`cscart_product_descriptions`.`product_id` in (90712,90718,90586,90587,90730,90731,90616,90617,90622,90623,90724,90726,90716,90722,90592,90593,92534,89243,89244,89253,89254,90588,90590,90657,90642,92533,90664,90665,90670,90671)) and (`nuie_scalesta_net`.`cscart_product_descriptions`.`lang_code` = 'en'))"
    }
  }
}

Result

product_id short_description full_description
89243 nuie Shower Baths 1700mm Left Hand Square Shower Bath Set
89244 nuie Shower Baths 1700mm Right Hand Square Shower Bath Set
89253 nuie Shower Baths 1500mm Left Hand Square Shower Bath Set
89254 nuie Shower Baths 1500mm Right Hand Square Shower Bath Set
90586 Nuie 1700 B-Bath Panel & Chrome Screen - Left Hand
90587 Nuie 1700 B-Bath Panel & Chrome Screen - Right Hand
90588 Nuie 1700 P-Bath Panel & Chrome Screen - Left Hand
90590 Nuie 1700 P-Bath Panel & Chrome Screen - Right Hand
90592 Nuie 1700 P-Bath Panel & Black Screen - Left Hand
90593 Nuie 1700 P-Bath Panel & Black Screen - Right Hand
90616 Nuie 1700x700 Eternalite Bath Panel & Screen
90617 Nuie 1700x700 Eternalite Bath Panel & Screen
90622 Nuie 1700x700 Eternalite Bath Panel & Screen
90623 Nuie 1700x700 Eternalite Bath Panel & Screen
90642 Nuie 1700x700 Standard Bath Panel & Screen
90657 Nuie 1700x700 Standard Bath Panel & Screen
90664 Nuie 1700x750 Standard Bath Panel & Screen
90665 Nuie 1700x750 Standard Bath Panel & Screen
90670 Nuie 1700x750 Standard Bath Panel & Screen
90671 Nuie 1700x750 Standard Bath Panel & Screen
90712 Nuie 1700 Square Bath Panel & Chrome Screen - Left Hand
90716 Nuie 1700 Square Bath Panel & Chrome Screen - Left Hand
90718 Nuie 1700 Square Bath Panel & Chrome Screen - Right Hand
90722 Nuie 1700 Square Bath Panel & Chrome Screen - Right Hand
90724 Nuie 1700 Square Bath Panel & Black Screen - Left Hand
90726 Nuie 1700 Square Bath Panel & Black Screen - Right Hand
90730 Nuie 1700 Square Bath Panel & B/Brass Screen - Left Hand
90731 Nuie 1700 Square Bath Panel & B/Brass Screen - Right Hand
92533 nuie Freestanding Double Ended Boat Bath Tub, 1555mm x 745mm - White
92534 nuie Freestanding Double Ended Boat Bath Tub, 1655mm x 745mm - White