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 (
    89657, 88330, 88340, 88341, 88261, 88335, 
    88336, 88379, 88380, 89703, 89721, 
    88333, 89656, 89698, 89655, 86874, 
    88375, 88376, 88331, 88332, 88339, 
    88370, 88371, 89697, 88328, 88327, 
    88329, 88326, 86872, 88368
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00078

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 (89657,88330,88340,88341,88261,88335,88336,88379,88380,89703,89721,88333,89656,89698,89655,86874,88375,88376,88331,88332,88339,88370,88371,89697,88328,88327,88329,88326,86872,88368)) and (`nuie_scalesta_net`.`cscart_product_descriptions`.`lang_code` = 'en'))"
    }
  }
}

Result

product_id short_description full_description
86872 nuie Leg Set Suitable for 1100-1200mm Rectangular Trays - Slate Grey
86874 nuie Leg Set Suitable for 1300-1800mm Rectangular & Walk in Trays - Slate Grey
88261 nuie Slip Resistant Square Slimline Shower Tray 760 x 760mm - White
88326 nuie Rectangular Slimline Shower Tray 900 x 700mm - White
88327 nuie Rectangular Slimline Shower Tray 900 x 760mm - White
88328 nuie Rectangular Slimline Shower Tray 900 x 800mm - White
88329 nuie Square Slimline Shower Tray 900 x 900mm - White
88330 nuie Rectangular Slimline Shower Tray 1200 x 700mm - White
88331 nuie Rectangular Slimline Shower Tray 1000 x 760mm - White
88332 nuie Rectangular Slimline Shower Tray 1000 x 800mm - White
88333 nuie Rectangular Slimline Shower Tray 1000 x 900mm - White
88335 nuie Rectangular Slimline Shower Tray 1100 x 700mm - White
88336 nuie Rectangular Slimline Shower Tray 1100 x 760mm - White
88339 nuie Rectangular Slimline Shower Tray 1000 x 700mm - White
88340 nuie Rectangular Slimline Shower Tray 1200 x 760mm - White
88341 nuie Rectangular Slimline Shower Tray 1200 x 800mm - White
88368 nuie Offset Quadrant Slimline Shower Tray Left Hand 900 x 760mm - White
88370 nuie Offset Quadrant Slimline Shower Tray Left Hand 900 x 800mm - White
88371 nuie Offset Quadrant Slimline Shower Tray Right Hand 900 x 800mm - White
88375 nuie Offset Quadrant Slimline Shower Tray Left Hand 1000 x 800mm - White
88376 nuie Offset Quadrant Slimline Shower Tray Right Hand 1000 x 800mm - White
88379 nuie Offset Quadrant Slimline Shower Tray Left Hand 1200 x 800mm - White
88380 nuie Offset Quadrant Slimline Shower Tray Right Hand 1200 x 800mm - White
89655 nuie Square Slimline Shower Tray 700 x 700mm - Slate Grey
89656 nuie Square Slimline Shower Tray 760 x 760mm - Slate Grey
89657 nuie Square Slimline Shower Tray 800 x 800mm - Slate Grey
89697 nuie Quadrant Slimline Shower Tray 700 x 700mm - Slate Grey
89698 nuie Quadrant Slimline Shower Tray 760 x 760mm - Slate Grey
89703 nuie Quadrant Slimline Shower Tray 800 x 800mm - Slate Grey
89721 nuie Leg Set & Plinth Kit (1700 & 1000 Panel) - Slate Grey