sql max函數錯誤：關鍵字“ select”附近的語法不正確

Question

我有下一個sql代碼，您可以在下面看到。 它可以正常工作，但條件所在的最后一行除外。

    select m.model,m.price from (
    select product.model, pc.price
    from product
    join pc 
    on product.model=pc.model
    union
    select product.model, laptop.price
    from product
    join laptop 
    on product.model=laptop.model
union
    select product.model, printer.price
    from product
    join printer 
    on product.model=printer.model
    ) m
    where m.price = select max(m.price) from m

我遇到下一個錯誤：關鍵字“選擇”附近的語法不正確。 如果我把最后一行where m.price = m.price ： where m.price = m.price它也可以工作

Answer 1

您是否追求最高的價格？

select m.model,MAX(m.price) as price from 
(
    select product.model, pc.price
    from product
    join pc 
    on product.model=pc.model
    union
    select product.model, laptop.price
    from product
    join laptop 
    on product.model=laptop.model
union
    select product.model, printer.price
    from product
    join printer 
    on product.model=printer.model
    ) m
GROUP BY m.model

Answer 2

如果您正在尋找價格最高的型號：

select m.model, m.price
from (select p.model, pc.price
      from product p join
           pc 
           on p.model = pc.model
      union all
      select p.model, laptop.price
      from product join
           laptop 
           on p.model = laptop.model
      union all
      select p.model, printer.price
      from product p join
           printer 
           on p.model = printer.model
    ) m
order by m.price desc
limit 1;

但是，這是非常復雜的方法，因為不需要join ：

select m.model, m.price
from (select pc.model, pc.price
      from pc 
      union all
      select laptop.model, laptop.price
      from laptop 
      union all
      select printer.model, printer.price
      from printer 
    ) m
order by m.price desc
limit 1;