如何从 table 中 select 并将值除以 PostgreSQL 中另一个查询的结果？

Question

考虑一下我有这个 table:

create table currency(
currency            char(3)                 
                    PRIMARY KEY,

rate                decimal,                

buy                 decimal,                 

sell                decimal                 


);

我有这个数据：

insert into currency(currency,rate,buy,sell) values('EUR', 1, 1, 1);
insert into currency(currency,rate,buy,sell) values('USD',  0.8979, 0.901, 0.887);
insert into currency(currency,rate,buy,sell) values('GBP', 1.12404, 1.14405, 1.10543);

现在我想 select 基于美元汇率的汇率，然后我希望所有行的汇率、买入和卖出列除以美元汇率。即

我想要类似的东西

select currency, rate/<usd exchange rate>, buy/<usd exchange rate>, sell/<usd exchange rate>  from currency;

可以select编辑为：

select rate from currency where currency='USD';

Answer 1

您可以在一次查询中从 table 中获取两次：

SELECT c.currency, c.rate / u.rate AS rate, c.buy / u.rate AS buy, c.sell / u.rate AS sell 
FROM currency c, currency u 
WHERE u.currency='USD';

将在完整的 table 和美元行之间进行交叉连接。

如何从 table 中 select 并将值除以 PostgreSQL 中另一个查询的结果？

How to select from a table and divide the values with the result of another query in PostgreSQL?

sql

postgresql

postgresql-9.4