Question

我正在尝试使用子查询来查询我们的订单数据库并返回3列，例如：

Date          Orders          Replacements
09-MAY-14     100             5
...           ...             ...

创建的每个订单都有一个理由，这基本上意味着它是一个替代产品，即没有理由的订单是新订单，有理由的订单是替换订单。

我正在使用下面的查询来尝试获取此信息，但是我收到了很多错误消息，每次我认为我修复了一个我创建了另外10个，所以假设我完全有错误的想法这里。

SELECT Orders.EntryDate AS "Date", COUNT(Orders.OrderNo) AS "Orders",
  (SELECT COUNT(Orders.OrderNo) AS "Replacements"
  FROM Orders
  WHERE Orders.Reason IS NOT NULL
  AND Orders.EntryDate = '09-MAY-2014'
  AND Orders.CustomerNo = 'A001'
  GROUP BY Orders.EntryDate
  )
FROM Orders
WHERE Orders.Reason IS NULL
AND Orders.EntryDate = '09-MAY-2014'
AND Orders.CustomerNo = 'A001'
GROUP BY Orders.EntryDate
;

Answer 1

为什么子查询使用大小写！

SELECT Orders.EntryDate AS "Date", COUNT(Orders.OrderNo) AS "Orders",
sum(CASE WHEN Orders.reason is null then 1 else 0 end) as "Replacements"
FROM Orders
WHERE Orders.Reason IS NULL
AND Orders.EntryDate = '09-MAY-2014'
AND Orders.CustomerNo = 'A001'
GROUP BY Orders.EntryDate

子查询必须每次执行，因为您需要评估案例可以为您执行的每条记录，然后对结果求和。如果您需要计算一些非替换订单，那么只需执行不同的情况而不是计数。

Answer 2

您的错误可能是由于您未在子group by子句中包含子查询。您可以尝试这种方法，但这个方法更简单：

select entrydate "date"
, count(orderno) "orders"
, sum(case when reason is not null then 1 else 0 end) "replacements"
etc
group by entrydate

Answer 3

您可以将case表达式加起来，而不是使用另一个子查询和另一个where子句：

SELECT   Orders.EntryDate AS "Date", 
         SUM (CASE WHEN Orders.Reason IS NULL THEN 1 ELSE 0 END) AS "Orders",
         SUM (CASE WHEN Orders.Reason IS NOT NULL THEN 1 ELSE 0 END) AS "Replacements"
FROM     Orders
WHERE    Orders.EntryDate = '09-MAY-2014'
AND      Orders.CustomerNo = 'A001'
GROUP BY Orders.EntryDate

Answer 4

这是你想要做的吗？

SELECT Orders.EntryDate , COUNT(case when Orders.reason is null then 1 end) AS orders , COUNT(case when Orders.reason is not null then 1 end) AS Replacements FROM Orders WHERE Orders.EntryDate = '09-MAY-2014' AND Orders.CustomerNo = 'A001' GROUP BY Orders.EntryDate

Replacements表达式可以简化为：

COUNT(Orders.reason)

如何使用SQL子查询？

4 个答案: