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我有一个相当复杂的查询，因为我试图将数学排除在应用程序代码和查询之外。我试图在选择中设置一个变量，然后在同一个选择中重新使用它。不幸的是，我使用这些变量的任何列都在应该有数据的地方返回 null。其他一切工作正常。

SELECT @signups:= COUNT(registrations.id) as signups, 
      @registrations:= SUM(IF(registrations.fees_paid_by_users = '1', registrations.amount - registrations.databar_fees - registrations.taxes - registrations.extras_price + registrations.discount_total, registrations.amount - registrations.taxes - registrations.extras_price + registrations.discount_total)) as registrations,
      @activities:= SUM(registrations.extras_price) as activities,
      @coupons:= SUM(discount_total) as coupons,
      @subtotal:= @registrations + @activities - @coupons as subtotal,
      @fees_not_paid_by_user:= SUM(IF(registrations.fees_paid_by_users = '0', registrations.databar_fees, 0)) as fees_not_paid_by_user,
      @taxes:= SUM(registrations.taxes) as taxes,
      @total_including_taxes:= @subtotal - @fees_not_paid_by_user + @taxes as total_including_taxes,
       events.name, 
       event_forms.title ,
       event_forms.id,
       CONCAT(users.first_name, ' ', users.last_name) as user_name
FROM registrations, 
     events, 
     event_forms, 
     transactions,
     users
WHERE transactions.date >= '2013-09-01 00:00:00' 
AND transactions.date <= '2013-09-30 23:59:59'
AND registrations.transaction_id = transactions.id
AND registrations.event_forms_id = event_forms.id
AND event_forms.event_id = events.id
AND events.owner_id = users.id
GROUP BY registrations.event_forms_id
ORDER BY user_name ASC, name ASC, title ASC

在上面的查询中，subtotal和total_including_taxes列返回 null，我假设是因为查询无法访问先前定义的变量。

这是我第一次真正使用 MySQL 的用户变量（我是开发人员，而不是 DBA），我不确定我是否做错了什么，如果是，如何修复它。如果需要，我可以在代码中进行数学运算，但我真的很想将它保留在数据库服务器上，因为它比应用程序服务器更强大，并且可以更轻松地处理这个问题。

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2 回答 2

0

Given your query, you're doing SUM(SUM(...)). SUM's intended for adding together field values, and I kind of doubt that variables will do the same thing e.g..

SELECT ..
   @foo := SUM(...),
   @bar := SUM(@foo)

might as well just be

   @bar := @bar + @foo
于 2013-10-01T21:22:00.843 回答
0

不幸的是，查询中的先前变量是未定义的。您将不得不替换公式而不是它们。或者在代码中计算下一个变量。

于 2013-10-02T17:21:50.210 回答