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 (
    89430, 89123, 89127, 89159, 89550, 83087, 
    89437, 91289, 89157, 89548, 90092, 
    90102, 90111, 82329, 86813, 86847, 
    89100, 83114, 83124, 83133, 90119, 
    83085, 89121, 89162, 89553, 89125, 
    89198, 86812, 89099, 82331
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00074

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 (89430,89123,89127,89159,89550,83087,89437,91289,89157,89548,90092,90102,90111,82329,86813,86847,89100,83114,83124,83133,90119,83085,89121,89162,89553,89125,89198,86812,89099,82331)) and (`nuie_scalesta_net`.`cscart_product_descriptions`.`lang_code` = 'en'))"
    }
  }
}

Result

product_id short_description full_description
82329 Hudson Reed Tec Pura Triple Thermostatic Shower Valve - Chrome
82331 Hudson Reed Tec Pura Twin Thermostatic Shower Valve With Diverter - Chrome
83085 Hudson Reed Art Twin Thermostatic Shower Valve With Diverter - Chrome
83087 Hudson Reed Art Triple Thermostatic Shower Valve - Chrome
83114 nuie Arvan Triple Thermostatic Valve - Matt Black
83124 nuie Arvan Triple Thermostatic Valve - Gunmetal
83133 nuie Arvan Triple Thermostatic Valve - Brushed Brass
86812 nuie Square Showers Twin Thermostatic Shower Valve With Diverter - Chrome
86813 nuie Square Showers Triple Thermostatic Shower Valve - Chrome
86847 Hudson Reed Tec Crosshead Triple Thermostatic Shower Valve - Chrome
89099 nuie Round Showers Twin Thermostatic Shower Valve With Diverter - Chrome
89100 nuie Round Showers Triple Thermostatic Shower Valve - Chrome
89121 Hudson Reed Reign Twin Valve With Diverter - Chrome
89123 Hudson Reed Reign Triple Thermostatic Shower Valve - Chrome
89125 Hudson Reed Reign Twin Valve With Diverter - Chrome
89127 Hudson Reed Reign Triple Thermostatic Shower Valve - Chrome
89157 Hudson Reed Indus Twin Thermostatic Shower Valve With Diverter - Chrome
89159 Hudson Reed Round Valves Triple Valve - Chrome
89162 Hudson Reed Round Valves Twin Valve with Diverter - Chrome
89198 nuie Sanford Triple Thermostatic Valve - Chrome
89430 Hudson Reed Industrial Valves Triple Valve - Chrome
89437 Hudson Reed Industrial Valves Twin Valve with Diverter - Chrome
89548 Hudson Reed Lennox Twin Thermostatic Shower Valve With Diverter - Chrome
89550 Hudson Reed Square Valves Triple Valve - Chrome
89553 Hudson Reed Square Valves Twin Valve with Diverter - Chrome
90092 nuie Windon Triple Thermostatic Valve - Matt Black
90102 nuie Windon Triple Thermostatic Valve - Gunmetal
90111 nuie Windon Triple Thermostatic Valve - Brushed Brass
90119 nuie Windon Triple Thermostatic Valve - Chrome
91289 nuie Aztec Triple Thermostatic Concealed Shower Valve - 2 Outlet - Matt Black