从条件表获取WHERE子句的条件

Question

我创建了以下简单的DataModel：

我用以下数据填充了表格：

1）表客户

INSERT INTO test.customer
(CustomerName, Country, RegistrationDate)
VALUES 
("Customer A","DE","2015-05-03"),
("Customer B","US","2015-07-25"), 
("Customer C","US","2016-02-15"), 
("Customer D","DE","2017-09-21"), 
("Customer E","AU","2018-12-07");

2）表订单

INSERT INTO test.orders
(idCustomer, PaymentMethod, OrderDate, OrderValue)
VALUES 
("1","CreditCard","2015-05-04","500"),
("1","PayPal","2015-11-18","200"), 
("3","PayPal","2017-09-04","300"), 
("2","Invoice","2018-04-30","100");

3）表条件

INSERT INTO test.criterias
(Country, MinimumOrderValue)
VALUES 
("DE","300"),
("US","150"), 
("AU","200");

然后，我根据条件Customers和Orders创建了一个查询，以获取Country及其OrderValue：

SELECT 
test.customer.idCustomer, CustomerName, Country,
test.orders.OrderValue

FROM test.customer
LEFT JOIN test.customer_info ON test.customer.idCustomer = test.customer_info.idCustomer
LEFT JOIN test.orders ON test.customer.idCustomer = test.orders.idCustomer

WHERE 
Country = "US" AND OrderValue >= "150"
OR Country = "DE" AND OrderValue >= "300" 
OR country = "AU" AND OrderValue >= "200";

到目前为止，所有这些都工作正常。

---

但是，与其将条件放在SQL查询的WHERE子句中，不应该将它们存储在名为Criterias的单独表中。然后，查询应该从该表中获取数据，并像上面的查询中一样完全应用它们。

要实现此目的，我需要在代码中进行哪些更改？

Answer 1

不一定是答案；评论太久了...

一组有效的查询条件可能看起来像这样...

 WHERE (country = "US" AND OrderValue >= 150)
    OR (country = "DE" AND OrderValue >= 300)
    OR (country = "AU" AND OrderValue >= 200);

...或者实际上（尽管可能更慢）...

WHERE (country,ordervalue) IN(('US',150),('DE',300),('AU',200));

Answer 2

根据上述数据库架构，您必须制作一个主要客户字段客户表，它将按照表名顺序进行映射。之后，您需要在查询中使用Join and exist子句。

select c.cutomerId, c.customerName, c.country, o.orderValue from customer c, order o where  c.customerId = o.customerId and 
        exists (select * from criteria cr where cr.country = c.country and o.order >= cr.MinimumOrderValue)

Answer 3

您只需join表或在where子句中使用子查询。

后者更易于键入，因此：

WHERE EXISTS (SELECT 1
              FROM Criterias cr
              WHERE cr.Country = c.Country AND
                    cr.MinOrderValue <=  o.OrderValue
             )