Sql 比较查询

我试图编写一个查询来比较两个日期范围的数据

第一个日期范围：

select code,description, quantity*each as Total
from orderiteminfo oi, orderinfo o, invoiceinfo i
where oi.orderid = o.orderid
and o.invoiceid = i.invoiceid
and i.invdate between '2014-01-01' and '2014-02-01'
group by oi.code, description, quantity, each

select code,description, quantity*each as Total
from orderiteminfo oi, orderinfo o, invoiceinfo i
where oi.orderid = o.orderid
and o.invoiceid = i.invoiceid
and i.invdate between '2015-01-01' and '2015-02-01'
group by oi.code, description, quantity, each

第二个日期范围：

select code,description, quantity*each as Total
from orderiteminfo oi, orderinfo o, invoiceinfo i
where oi.orderid = o.orderid
and o.invoiceid = i.invoiceid
and i.invdate between '2014-01-01' and '2014-02-01'
group by oi.code, description, quantity, each

select code,description, quantity*each as Total
from orderiteminfo oi, orderinfo o, invoiceinfo i
where oi.orderid = o.orderid
and o.invoiceid = i.invoiceid
and i.invdate between '2015-01-01' and '2015-02-01'
group by oi.code, description, quantity, each

我希望结果是：

---

Code | Description | Total for First Date Range | Total for second Date Range

如果我理解正确，我认为您可以在单个查询中使用case当语句：

select code,
       description, 
       case 
          when i.invdate between '2014-01-01' and '2014-02-01'
            then quantity*each 
        end  Total_for_First_Date_Range,
        case 
          when i.invdate between '2015-01-01' and '2015-02-01'
            then quantity*each 
        end  Total_for_Second_Date_Range              
from orderiteminfo oi, orderinfo o, invoiceinfo i
where oi.orderid = o.orderid
and o.invoiceid = i.invoiceid 
group by oi.code, description, quantity, each; --not sure if you need this

像这样的

SELECT code,
       description,
       SUM(CASE
             WHEN i.invdate BETWEEN '2014-01-01' AND '2014-02-01' THEN quantity * each
           END) AS [Total for First Date Range],
       SUM(CASE
             WHEN i.invdate BETWEEN '2015-01-01' AND '2015-02-01' THEN quantity * each
           END) AS [Total for second Date Range]
FROM   orderiteminfo oi
       INNER JOIN orderinfo o
               ON oi.orderid = o.orderid
       INNER JOIN invoiceinfo i
               ON o.invoiceid = i.invoiceid
WHERE  ( i.invdate BETWEEN '2014-01-01' AND '2014-02-01'
          OR i.invdate BETWEEN '2015-01-01' AND '2015-02-01' )
GROUP  BY oi.code,
          description 

---

作为旁注，总是使用

内部连接

语法来连接两个表，而不是老式的逗号分隔连接，并且在

Where

子句中单独保留过滤器，这更易于阅读

如果我们随着时间的推移添加或删除代码，那么在两个日期范围中也可能没有完全相同的代码。因此，我在我的原始查询我需要显示每个oi.code的总和（数量*每个）。我将如何修改此查询？