Mysql 平均售价中的排序语句

Question

Write one (1) MySQL query statement that returns the average sale price for properties that were 'under contract' in the past month for each State where the agency operates. The result should be sorted from highest to lowest by average sale price. Your query should return a table in the following format i tried

select * from(
select   avg(sale_price)  from  purchase where property_id = 64
union all  (
select   avg(sale_price)  from  purchase where property_id = 60)
union (
select avg(sale_price) from purchase where property_id = 58))  as i
order by  sale_price  ASC;

i got this error as i have sale_price column in my table

22:08:19 select * from( select avg(sale_price) from purchase where property_id = 64 union all ( select avg(sale_price) from purchase where property_id = 60) union ( select avg(sale_price) from purchase where property_id = 58)) as i order by sale_price ASC LIMIT 0, 1000 Error Code: 1054. Unknown column 'sale_price' in 'order clause' 0.000 sec

Answer 1

You should use an alias in the SELECT clause in every UNION.

SELECT 
  * 
FROM
  (SELECT 
    AVG(sale_price) AS sale_price 
  FROM
    purchase 
  WHERE property_id = 64 
  UNION
  ALL 
  (SELECT 
    AVG(sale_price)  AS sale_price 
  FROM
    purchase 
  WHERE property_id = 60) 
  UNION
  (SELECT 
    AVG(sale_price)  AS sale_price
  FROM
    purchase 
  WHERE property_id = 58)) AS i 
ORDER BY sale_price ASC ;

Or could you use the following query? I would think this is more straightforward on performance side.

SELECT 
  AVG(sale_price) AS avg_sale_price 
FROM
  purchase 
WHERE property_id IN (64, 60, 58) 
GROUP BY property_id 
ORDER BY avg_sale_price ;