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 (
    96974, 96975, 96976, 96977, 96978, 96979, 
    96980, 98509, 98510, 98511, 98512, 
    98513, 98514, 98516, 98517, 98518, 
    98519, 98520, 98889, 98890, 98891, 
    98892, 98893, 98894, 98895, 98896, 
    98898, 98899, 98900, 98901
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00067

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 (96974,96975,96976,96977,96978,96979,96980,98509,98510,98511,98512,98513,98514,98516,98517,98518,98519,98520,98889,98890,98891,98892,98893,98894,98895,98896,98898,98899,98900,98901)) and (`nuie_scalesta_net`.`cscart_product_descriptions`.`lang_code` = 'en'))"
    }
  }
}