只选一条记录

Question

已搜索hi and low，似乎无法找到如何做到这一点。我有一个两列的表。

Order route 
===== ===== 
Order_1 100 
Order_1 101 
Order_2 102 
Order_3 103 
Order_4 104 

我想要的结果是，提前

Order_2 102 
Order_3 103 
Order_4 104 

感谢。

Answer 1

Order是保留关键字，所以我用order_column代替。

首先，测试数据：

create table order_route_table(order_column varchar2(20) 
    , route number); 

insert into order_route_table 
select 'Order_1', 100 from dual 
union all select 'Order_1', 101 from dual 
union all select 'Order_2', 102 from dual 
union all select 'Order_3', 103 from dual 
union all select 'Order_4', 104 from dual; 

然后传统上：

select order_column, min(route) 
from order_route_table 
group by order_column 
having count(*) = 1; 

与分析：

select order_column, route 
from (select order_column 
     , route 
     , count(*) over (partition by order_column) as order_count 
    from order_route_table) 
where order_count = 1; 

结果在任一种情况下：

ORDER_COLUMN    ROUTE 
-------------------- ---------- 
Order_2      102 
Order_3      103 
Order_4      104