两张表合并后，如何按两张表中列名相同的列排序？

Question

这是两张表。

Create table If Not Exists Customers (Id int, Name varchar(255));
Create table If Not Exists Orders (Id int, CustomerId int);
insert into Customers (Id, Name) values ('1', 'Joe');
insert into Customers (Id, Name) values ('2', 'Henry');
insert into Customers (Id, Name) values ('3', 'Sam');
insert into Customers (Id, Name) values ('4', 'Max');
insert into Orders (Id, CustomerId) values ('1', '3');
insert into Orders (Id, CustomerId) values ('2', '1');
insert into Orders (Id, CustomerId) values ('3', '5');
insert into Orders (Id, CustomerId) values ('4', '6');

我把两张表的左联接和右联接结合起来了

select *
from customers as c
left join orders as o
on c.id = o.customerid

union

select *
from customers as c
right join orders as o
on c.id = o.customerid;

但我想按表customers中的id来排列结果集。

select
*
from
customers as c
left join
orders as o
on
c.id = o.customerid

union

select
*
from
customers as c
right join
orders as o
on
c.id = o.customerid
order by
c.id;

但是MySQL的响应是 "错误代码: 1250. 表'c'从一个SELECTs不能用于全局ORDER子句"。于是我把代码改成。

select
*
from
customers as c
left join
orders as o
on
c.id = o.customerid

union

select
*
from
customers as c
right join
orders as o
on
c.id = o.customerid
order by
id;

但是MySQL的响应是 "错误代码： 1052. 订单子句中的'id'列含糊不清"。

我真的明白这两个响应，但我还想知道联合后如何从客户中按id排序？

Answer 1

是的，你需要一个全局排序，通过使当前查询的子查询，通过别名ID列单独。

select *
  from
  (
   select c.id as c_id, c.name, o.id as o_id, o.CustomerId
     from customers as c
     left join orders as o
       on c.id = o.customerid
    union    
   select c.id as c_id, c.name, o.id as o_id, o.CustomerId
     from customers as c
    right join orders as o
       on c.id = o.customerid    
  ) q
 order by q.c_id  

Answer 2

也许你需要在这。

(
select c.id c_id, c.name, o.id o_id
from Customers as c
left join Orders as o on c.id = o.customerid
)
union
(
select o.customerid, c.name, o.id
from Customers as c
right join Orders as o on c.id = o.customerid
)
order by c_id;

fiddle