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 (
    84036, 88933, 89011, 89523, 90109, 91308, 
    91893, 91894, 91895, 92050, 92138, 
    92337, 92338, 92339, 92340, 83954, 
    83956, 83958, 83960, 90061, 85531, 
    89623, 89636, 83978, 83979, 83980, 
    83981, 90106, 88936, 89648
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00105

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 (84036,88933,89011,89523,90109,91308,91893,91894,91895,92050,92138,92337,92338,92339,92340,83954,83956,83958,83960,90061,85531,89623,89636,83978,83979,83980,83981,90106,88936,89648)) and (`nuie_scalesta_net`.`cscart_product_descriptions`.`lang_code` = 'en'))"
    }
  }
}