Sql 在Oracle中检索具有一个条目的行

我有一个表订单，其中有许多销售订单和许多客户，通常是同一客户的许多订单。但我试图找到针对单个客户的订单，我不想看到针对同一客户的多个订单。我的例子可能会有所帮助

╔══════════╦══════════════╗
║ Customer ║ Order Number ║
╠══════════╬══════════════╣
║   ABC    ║     123      ║
║   ABC    ║     456      ║
║   XYZ    ║     789      ║
║   MNO    ║     987      ║
║   XYZ    ║     654      ║
╚══════════╩══════════════╝

---

因此，在本例中，我只想看到客户MNO和订单号987，因为该客户只有一个条目。

Hmmm，您可以使用聚合来完成此操作：

select customer, min(OrderNumber) as OrderNumber
from t
group by customer
having count(*) = 1;

只有一行时，min返回该行上的订单号

另一种方法不存在：

---

这样做的好处是可以检索更多的列。

请尝试以下方法

with tbl (Customer,Order_Number) as
(select 'ABC',123 from dual union all
select 'ABC',456 from dual union all
select 'XYZ',789 from dual union all
select 'MNO',987 from dual union all
select 'XYZ',654 from dual)
 --recreating the source table
select customer,Order_Number from (
select t.*, count(customer) over (partition by customer) as cnt from tbl t)
where cnt =1

with tbl (Customer,Order_Number) as
(select 'ABC',123 from dual union all
select 'ABC',456 from dual union all
select 'XYZ',789 from dual union all
select 'MNO',987 from dual union all
select 'XYZ',654 from dual)
 --recreating the source table
select customer,Order_Number from (
select t.*, count(customer) over (partition by customer) as cnt from tbl t)
where cnt =1