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 (
    91444, 85727, 85744, 85754, 85764, 88770, 
    88198, 88210, 88235, 88239, 90836, 
    88757, 89452, 89465, 89473, 89481, 
    85734, 89969, 90839, 90841, 91535, 
    87505, 87521, 88454, 88471, 88487, 
    88242, 88246, 89457, 89021
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00101

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 (91444,85727,85744,85754,85764,88770,88198,88210,88235,88239,90836,88757,89452,89465,89473,89481,85734,89969,90839,90841,91535,87505,87521,88454,88471,88487,88242,88246,89457,89021)) and (`nuie_scalesta_net`.`cscart_product_descriptions`.`lang_code` = 'en'))"
    }
  }
}

Result

product_id short_description full_description
85727 Hudson Reed Fluted 600mm Wall Hung 2-Drawer Unit - Satin Anthracite
85734 Hudson Reed Fluted 600mm Wall Hung 2-Drawer Unit - Satin White
85744 Hudson Reed Fluted 600mm Wall Hung 2-Drawer Unit - Satin Grey
85754 Hudson Reed Fluted 600mm Wall Hung 2-Drawer Unit - Satin Blue
85764 Hudson Reed Fluted 600mm Wall Hung 2-Drawer Unit - Satin Green
87505 nuie Athena Floor Standing 2 Drawer Vanity Unit 800mm - Anthracite Woodgrain
87521 nuie Athena Floor Standing 2 Drawer Vanity Unit 800mm - Hacienda Black
88198 Hudson Reed Juno 600mm Wall Hung 2-Drawer Unit - Graphite Grey
88210 Hudson Reed Juno 600mm Wall Hung 2-Drawer Unit - Coastal Grey
88235 Havana Components Wall Hung 2 Drawer Unit, 600mm - Graphite Grey
88239 Havana Components Wall Hung 2 Drawer Unit, 600mm - Coastal Grey
88242 Havana Components Wall Hung 2 Drawer Unit, 500mm - Metallic Slate
88246 Havana Components Wall Hung 2 Drawer Unit, 500mm - Autumn Oak
88454 nuie Arno 800mm Floor Standing 2-Drawer Unit - Solace Oak
88471 nuie Arno 800mm Floor Standing 2-Drawer Unit - Anthracite
88487 nuie Arno 800mm Floor Standing 2-Drawer Unit - Charcoal Black
88757 Hudson Reed Fusion Fitted Floor Standing 2 Door Vanity Unit 600mm - Gloss Grey
88770 Hudson Reed Fusion Wall Hung 2 Drawer Vanity Unit 500mm - Gloss Grey
89021 nuie Mayford Floor Standing 3 Door 2 Drawer Vanity Unit 1050mm - Gloss White
89452 Lunar Components Wall Hung 2 Drawer Unit, 600mm - Satin Anthracite
89457 Lunar Components Wall Hung 2 Drawer Unit, 600mm - Satin White
89465 Lunar Components Wall Hung 2 Drawer Unit, 600mm - Satin Grey
89473 Lunar Components Wall Hung 2 Drawer Unit, 600mm - Satin Blue
89481 Lunar Components Wall Hung 2 Drawer Unit, 600mm - Satin Green
89969 Hudson Reed Urban 800mm Wall Hung 2-Drawer Unit - Satin Green
90836 Hudson Reed Urban 800 F/S 2-Door Unit - Satin White
90839 Hudson Reed Urban 800 W/H 2-Drawer Unit - Satin Grey
90841 Hudson Reed Urban 800 W/H 2-Drawer Unit - Satin Blue
91444 600 FS 2-DRAWER UNIT (365 Deep)
91535 800 W/H 2-Drawer Unit