Question

我有两张这样的表：

  New_Customer     Order_Id     Invoice
  Aaron            5             5
  John             56            44
  --------------------------  
  Old_Customers    Order_Id     Ticket_Num
  Casey            44            11
  Jonathan          1            4

我想要什么？

  All_Customers    All_Order_Ids
  Aaron            5
  John             56
  Casey            44
  Jonathan         1

我可以仅使用一个select语句获得这两个列的联合（没有其他列）吗？

我试过

   select tb1.New_Customer union tb2.Old_Customers as All_Customers, tb1.Order_Id union tb2.Order_Id as All_Order_Ids;

但是我在语法问题上遇到错误。有人能告诉我我做错了吗？

Answer 1

使用第一个语句中显示的列别名执行2个select语句的UNION。这些别名将被选中并在结果集中使用。

create table t1
(   new_customer varchar(30) not null,
    order_id int not null,
    invoice int not null
);
insert t1 values ('aaron',5,5),('john',56,44);

create table t2
(   old_customers varchar(30) not null,
    order_id int not null,
    ticket_num int not null
);
insert t2 values ('casey',44,11),('jonathan',1,4);

查询：

select new_customer as All_Customers,order_id as All_Order_Ids from t1 
union 
select old_customers,order_id from t2 

+---------------+---------------+
| All_Customers | All_Order_Ids |
+---------------+---------------+
| aaron         |             5 |
| john          |            56 |
| casey         |            44 |
| jonathan      |             1 |
+---------------+---------------+

从多个列组合

1 个答案:

查询：