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 (
    86891, 91868, 92227, 92210, 85577, 85576, 
    85584, 85592, 85571, 85573, 85574, 
    91877, 91878, 91879, 91880, 91881, 
    91882, 91883, 85555, 85594, 85564, 
    90025, 85575, 86889, 87888, 92185, 
    85561, 86893, 85553, 85559
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00083

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 (86891,91868,92227,92210,85577,85576,85584,85592,85571,85573,85574,91877,91878,91879,91880,91881,91882,91883,85555,85594,85564,90025,85575,86889,87888,92185,85561,86893,85553,85559)) and (`nuie_scalesta_net`.`cscart_product_descriptions`.`lang_code` = 'en'))"
    }
  }
}

Result

product_id short_description full_description
85553 nuie Wastes & Extras Push Button Bath Waste - Chrome
85555 Easyclean Sprung Plug Bath Wst Min OF
85559 nuie Wastes & Extras Bath Waste - Chrome
85561 Retainer Bath Waste Brass & Link Chain
85564 nuie Wastes & Extras Pop Up Bath Waste - Chrome
85571 nuie Wastes & Extras Click Clack Bath Waste With Easyclean Removable Grid - Matt Black
85573 nuie Wastes & Extras Click Clack Bath Waste With Easyclean Removable Grid - Brushed Gun Metal
85574 Easyclean Sprung Plug Bath Waste
85575 nuie Wastes & Extras Pop Up Bath Waste - Chrome
85576 Extended Retainer Bath Waste & Overflow
85577 nuie Wastes & Extras Pop Up Bath Waste - Chrome
85584 Classic Concealed Bath Waste & Overflow
85592 Square Sprung Plug Bath Waste
85594 nuie Wastes & Extras Push Button Bath Waste - Chrome
86889 Traditional Towel Ring
86891 Traditional Gallery Shelf
86893 Traditional Double Robe Hook
87888 nuie Baths Leg Set
90025 nuie Baths Bath Leg Set
91868 BC Designs Victrion Double Towel Rail - Chrome
91877 BC Designs Victrion Double Robe Hook - Brushed Chrome
91878 BC Designs Victrion Double Robe Hook - Brushed Copper
91879 BC Designs Victrion Double Robe Hook - Brushed Gold
91880 BC Designs Victrion Double Robe Hook - Brushed Nickel
91881 BC Designs Victrion Double Robe Hook - Copper
91882 BC Designs Victrion Double Robe Hook - Gold
91883 BC Designs Victrion Double Robe Hook - Nickel
92185 BC Designs Bath Wastes Plug & Chain Concealed Bath Waste - Chrome
92210 BC Designs Bath Wastes Push Down Bath Waste 70mm (Slotted) - Chrome
92227 BC Designs Bath Wastes Push Down Bath Waste 60mm (Unslotted) - Chrome