Question

我的带有postgre数据库的rails应用程序，我正在尝试获取一些指标，并使用以下语句

Negotiation.find(:all, :conditions => conditions_hash('negotiation'), :select => 'sum(payment_term * amount_after_annualised_base) / sum(amount_after_annualised_base) as pt').first

如何确保sum（amount_after_annualised_base）不为0（因此不会抛出“除以零”错误）？

我发现了这一点，但不确定它是否正确/最佳/最有效的方式。

Negotiation.find(:all, :conditions => conditions_hash('negotiation'), :select => 'sum(payment_term * amount_after_annualised_base) / (CASE sum(amount_after_annualised_base) WHEN 0 THEN NULL ELSE sum(amount_after_annualised_base) END) as pt').first

谢谢！皮尔

Answer 1

使用nullif：

Negotiation.find(:all, :conditions => conditions_hash('negotiation'), :select => 'sum(payment_term * amount_after_annualised_base) / nullif(sum(amount_after_annualised_base),0) as pt').first

这只是解决方案的简洁速记：

Negotiation.find(:all, :conditions => conditions_hash('negotiation'), :select => 'sum(payment_term * amount_after_annualised_base) / (CASE sum(amount_after_annualised_base) WHEN 0 THEN NULL ELSE sum(amount_after_annualised_base) END) as pt').first

Answer 2

怎么样：

Negotiation.find(:all, 
                 :conditions => conditions_hash('negotiation'), 
                 :select => 'sum(amount_after_annualised_base) sum_amount,
                             sum(payment_term * amount_after_annualised_base) / greatest(1,sum_amount) as pt').first

如果sum_amount为零，请检查您的代码。

Answer 3

我认为你需要写一些像

这样的东西

Negotiation.find(
  :all, :conditions => conditions_hash('negotiation'), 
  :select => 'CASE sum(amount_after_annualised_base) WHEN 0 THEN NULL ELSE sum(payment_term * amount_after_annualised_base) / sum(amount_after_annualised_base) END as pt').first

如果sum(amount_after_annualised_base)为零，则返回NULL，否则执行请求的除法。

Rails：用postgres防止零除零

3 个答案: