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 (
    91905, 91906, 91907, 91908, 91909, 91910, 
    91911, 84268, 89735, 91904, 89435, 
    82417, 86852, 91921, 91922, 91923, 
    91924, 91925, 91926, 91927, 91929, 
    91930, 91931, 91932
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00072

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "10.82"
    },
    "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": 24,
      "rows_produced_per_join": 24,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "8.42",
        "eval_cost": "2.40",
        "prefix_cost": "10.82",
        "data_read_per_join": "91K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description"
      ],
      "attached_condition": "((`nuie_scalesta_net`.`cscart_product_descriptions`.`product_id` in (91905,91906,91907,91908,91909,91910,91911,84268,89735,91904,89435,82417,86852,91921,91922,91923,91924,91925,91926,91927,91929,91930,91931,91932)) and (`nuie_scalesta_net`.`cscart_product_descriptions`.`lang_code` = 'en'))"
    }
  }
}

Result

product_id short_description full_description
82417 Hudson Reed Tec Pura Triple Thermostatic Shower Valve With Diverter - Brushed Brass
84268 Old London Black Topaz Triple Exposed Shower Valve & Spout - Chrome / Black
86852 Hudson Reed Tec Crosshead Triple Thermostatic Shower Valve With Diverter - Brushed Brass
89435 Hudson Reed Industrial Valves Triple Valve with Diverter - Brushed Brass
89735 Old London White Topaz Triple Thermostatic Shower Valve With Rigid Riser - Chrome / White
91904 BC Designs Victrion Triple Exposed Thermostatic Valve, Spout Bath Filler and 8" Head - Chrome
91905 BC Designs Victrion Triple Exposed Thermostatic Valve, Spout Bath Filler and 8" Head - Brushed Chrome
91906 BC Designs Victrion Triple Exposed Thermostatic Valve, Spout Bath Filler and 8" Head - Brushed Copper
91907 BC Designs Victrion Triple Exposed Thermostatic Valve, Spout Bath Filler and 8" Head - Brushed Gold
91908 BC Designs Victrion Triple Exposed Thermostatic Valve, Spout Bath Filler and 8" Head - Brushed Nickel
91909 BC Designs Victrion Triple Exposed Thermostatic Valve, Spout Bath Filler and 8" Head - Copper
91910 BC Designs Victrion Triple Exposed Thermostatic Valve, Spout Bath Filler and 8" Head - Gold
91911 BC Designs Victrion Triple Exposed Thermostatic Valve, Spout Bath Filler and 8" Head - Nickel
91921 BC Designs Victrion Single Outlet Twin Thermostatic Exposed Valve - Brushed Chrome
91922 BC Designs Victrion Single Outlet Twin Thermostatic Exposed Valve - Brushed Copper
91923 BC Designs Victrion Single Outlet Twin Thermostatic Exposed Valve - Brushed Gold
91924 BC Designs Victrion Single Outlet Twin Thermostatic Exposed Valve - Brushed Nickel
91925 BC Designs Victrion Single Outlet Twin Thermostatic Exposed Valve - Copper
91926 BC Designs Victrion Single Outlet Twin Thermostatic Exposed Valve - Gold
91927 BC Designs Victrion Single Outlet Twin Thermostatic Exposed Valve - Nickel
91929 BC Designs Victrion Two Outlet Triple Thermostatic Concealed Valve - Brushed Chrome
91930 BC Designs Victrion Two Outlet Triple Thermostatic Concealed Valve - Brushed Copper
91931 BC Designs Victrion Two Outlet Triple Thermostatic Concealed Valve - Brushed Gold
91932 BC Designs Victrion Two Outlet Triple Thermostatic Concealed Valve - Brushed Nickel