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 (
    91457, 85729, 85746, 85756, 85766, 88987, 
    85736, 88771, 88174, 88222, 88243, 
    88247, 88758, 89964, 90838, 90840, 
    91530, 89454, 89467, 89475, 89483, 
    87450, 88200, 88212, 88236, 88240, 
    88503, 91445, 91459, 88678
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00086

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 (91457,85729,85746,85756,85766,88987,85736,88771,88174,88222,88243,88247,88758,89964,90838,90840,91530,89454,89467,89475,89483,87450,88200,88212,88236,88240,88503,91445,91459,88678)) and (`nuie_scalesta_net`.`cscart_product_descriptions`.`lang_code` = 'en'))"
    }
  }
}