Sql 如果不存在，则查询返回零

我有一张有货币、付款类型和发票金额的桌子。我必须编写查询以获取货币、paymenttype和总发票金额。这是非常简单的分组方式。但实际上我有三种付款类型0、1、2，表中的数据是

Currency.  Paymenttype invoice amount
Aaa.        0.           100
Aaa.        1.           200
Aaa.        1.            50
Bbb.        0.           150
Bbb.        1.           100
Bbb.        2.           100

我的查询是按货币、paymenttype从表组中选择货币、paymenttype、suminvoiceamount作为总计

结果

  Currency  paymenttype total
  Aaa.       0.           100
  Aaa.       1.           250
   Bbb.      0.           150
   Bbb.      1.           100
   Bbb.      2.           100

但我想要的是Aaa级。没有2个paymenttype is也应该显示一个值为0的行，如下所示

     Aaa.     2.     0

---

如何执行此操作？

您可以使用交叉联接生成所有行，然后联接所需的数据：

select c.currency, pt.paymenttype,
       coalesce(sum(i.invoiceamount), 0) as total
from currency c cross join
     paymenttype pt left join
     invoice i
     on i.currency = c.currency and i.paymenttype = pt.paymenttype
group by c.currency, pt.paymenttype;

---

您应该有一个包含所有类型的表

然后，您只需在payment\u type\u id上执行左连接，输出总数，如果没有，则为0

如果没有包含所有类型的表，则可以模拟它，但这将是一个肮脏的修复：

select a.currency, b.paymenttype, coalesce(sum(a.invoiceamount), 0)
from (select 0 as paymenttype,
      union all select 1 as paymenttype,
      union all select 2 as paymenttype) b
left join yourTable a on a.paymenttype = b.paymenttype
group by a.currency, b.paymenttype;

---

这对我的数据不起作用。虽然我的查询是select aa.Currency，aa.PaymentType，sumbb.amount from select*from select distinct PaymentType from payment交叉连接选择distinct Currency from payment c aa left join payment bb on aa.PaymentType=bb.PaymentType和aa.Currency=bb.Currency group by aa.PaymentType，aa.Currency订单by aa.Currency