Question

我可能无法正确理解我的条款，因此无法在网上找到答案。

我有2张这样的表

customer_db - Customer Data
CustomerID    CustomerName     CustomerContact
1             John             1234
2             Anna             5678
3             Angel            2468

customer_channel - Chat Channel Name
ChannelName            OnlineStatus
private-customer-1     YES
private-customer-2     NO

通常我会做这样的事情

Select a.OnlineStatus, b.CustomerName, b.CustomerContact FROM customer_db a,
customer_channel b WHERE a.CustomerID = b.ChannelName

如果有“私人 - 客户 - ”前缀，那么我就无法进行匹配。

我尝试添加前缀但不起作用。 如何选择在WHERE语句中向列名称添加“文本前缀”的表？

Select a.OnlineStatus, b.CustomerName, b.CustomerContact FROM customer_db a,
customer_channel b WHERE a.CustomerID = 'private-customer-'+b.ChannelName

Answer 1

使用concat函数，逗号（，）是一种旧方法，尝试使用join：

SELECT
    a.OnlineStatus,
    b.CustomerName,
    b.CustomerContact
FROM customer_db a
JOIN customer_channel b
ON a.CustomerID = concat('private-customer-', b.ChannelName)

Answer 2

在WHERE语句
中为列名添加'文本前缀'

不，除非您将其作为动态查询（预备语句），否则不能这样做。仅允许列或表名称别名使用前缀或后缀。

（或）您可以使用子查询并使用该子查询结果执行JOIN

Select a.OnlineStatus, 
b.CustomerName,
 b.CustomerContact 
FROM customer_db a JOIN ( select CustomerName, CustomerContact,
'private-customer-'+ ChannelName as channelName
from customer_channel ) b 
ON a.CustomerID = b.channelName;

Answer 3

尝试使用Concat函数..

  Select a.OnlineStatus,
         b.CustomerName, 
         b.CustomerContact 
  FROM customer_db a,
       customer_channel b 
  WHERE a.CustomerID = concat('private-customer-', b.ChannelName)

Answer 4

你可以使用replace或substring来做到这一点例如给出

drop table if exists a;
create table a(CustomerID  int,   CustomerName  varchar(5),   CustomerContact int);
insert into a values
(1,             'John' ,            1234),
(2,             'Anna' ,            5678),
(3,             'Angel',            2468);

drop table if exists b;
create table b (ChannelName varchar(20),            OnlineStatus  varchar(3));
insert into b values
('private-customer-1' ,    'YES'),
('private-customer-2' ,    'NO');

Select b.OnlineStatus, a.CustomerName, a.CustomerContact 
FROM   a
join  b on  a.CustomerID = replace(b.ChannelName,'private-customer-','');

Select b.OnlineStatus, a.CustomerName, a.CustomerContact 
FROM   a
join  b on  a.CustomerID = substring(b.ChannelName,18,length(b.channelname) -17)

两个查询都会导致

+--------------+--------------+-----------------+
| OnlineStatus | CustomerName | CustomerContact |
+--------------+--------------+-----------------+
| YES          | John         |            1234 |
| NO           | Anna         |            5678 |
+--------------+--------------+-----------------+

Mysql在Select语句中为列名添加前缀

4 个答案: