Question

select CURRENCY.currencyname, currency.currencysymbol, COUNTRYNAME.currencycode, 
       currency.exchangerate
from CURRENCY,COUNTRYNAME
where currency.currencycode=COUNTRYNAME.currencycode
having currency.exchangerate >= max(currency.exchangerate)
group by CURRENCY.currencyname, currency.currencysymbol, 
         COUNTRYNAME.currencycode, currency.exchangerate;

这是我得到的输出，我知道是错的，因为我试图只显示最大汇率。因此，任何帮助解决此查询将非常感激。我是oracle sql developer

CURRENCYNAME         CURRENCYSYMBOL       CURRENCYCODE EXCHANGERATE
-------------------- -------------------- ------------ ------------
British Pound        £                    GBP                     1,
US Dollar            $                    USD                1.9626 ,
Danish Krone         kr                   DKK                9.9918 ,
Malaysian Ringgit    RM                   MYR               6.35392 ,
Euro                 €                    EUR               1.34076 ,
Indian Rupee         Rs                   INR               77.3265 ,
Japanese Yen         ¥                    JPY               209.881,

Answer 1

尝试以下

SELECT CURRENCY.currencyname, currency.currencysymbol, 
       COUNTRYNAME.currencycode, MAX(currency.exchangerate) as ExchangeRate
FROM CURRENCY
INNER JOIN COUNTRYNAME ON COUNTRYNAME.currencycode = currency.currencycode
GROUP BY CURRENCY.currencyname, currency.currencysymbol, COUNTRYNAME.currencycode;

Answer 2

关于您的查询...

1。您无法将MAX（聚合）值与同一查询级别中的基值进行比较。您可以使用派生表（也称为“子查询”），例如

    select c.currencyname, c.currencysymbol, n.currencycode, c.exchangerate
    from CURRENCY c
    join COUNTRYNAME n on c.currencycode=n.currencycode
    where c.exchangerate = (select max(exchangerate) from currency)

2。您将从上面注意到我使用JOIN链接两个表。随着ANSI-92连接语法的出现，大约21年前，使用逗号列表的表名已经过时了。

3。您显示的查询无法正常工作。 GROUP BY子句位于HAVING子句之前，而不是之后。话虽如此，上面的第一点适用，你无法将MAX值与（基本）列值进行比较。

Answer 3

此查询可能简化为：

select max(currencyname), max(currencysymbol), currencycode, max(exchangerate)
from currency group by currencycode

（ - 假设没有任何国家从未使用的货币。）

在同一SQL语句中使用where和having时，查询输出错误

3 个答案: