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 (
    100521, 100522, 100523, 100524, 100525, 
    100526, 100527, 100528, 100529, 100530, 
    100531, 100532, 100533, 100534, 100535, 
    100642, 100644, 100646, 100648, 100789, 
    100790, 100791, 100792, 100793, 100794, 
    100795, 100796, 100797, 100798, 100799, 
    100800, 100801, 100802, 100803, 100804, 
    100805, 100806, 100807, 100808, 100809, 
    100810, 100811, 100812, 100813, 100814, 
    100815, 100816, 100817
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00091

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "21.63"
    },
    "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": 48,
      "rows_produced_per_join": 48,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "16.83",
        "eval_cost": "4.80",
        "prefix_cost": "21.63",
        "data_read_per_join": "183K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description"
      ],
      "attached_condition": "((`nuie_scalesta_net`.`cscart_product_descriptions`.`product_id` in (100521,100522,100523,100524,100525,100526,100527,100528,100529,100530,100531,100532,100533,100534,100535,100642,100644,100646,100648,100789,100790,100791,100792,100793,100794,100795,100796,100797,100798,100799,100800,100801,100802,100803,100804,100805,100806,100807,100808,100809,100810,100811,100812,100813,100814,100815,100816,100817)) and (`nuie_scalesta_net`.`cscart_product_descriptions`.`lang_code` = 'en'))"
    }
  }
}