mysql - 如何在 sql 查询的空字段中显示文本？

Question

我必须从数据库中提取客户列表，但如果第二个地址字段为空，我想显示文本 None Provided。这是我的查询:

    select concat(first_name, " ", last_name) as CustomerName, address, 
    address2, postal_code 
    from customer
    inner join address 
    using (address_id);

如果 address2 为空，我想显示“未提供”。我怎么做？我确信答案非常简单，但我脑袋放屁，到处都找不到答案。

好的，这就是我最终的结果:

    case when address2=" " or address2 is null then 'None Provided' 
    else address2 end as address2,

有没有更好的方法来实现这一点？

Answer 1

您可以使用CASE:

select concat(first_name, " ", last_name) as CustomerName, 
   address, 
   case when address2 is null then 'None Provided' else address2 end as address2, 
   postal_code 
from customer
inner join address 
using (address_id);

或者更好COALESCE :

select concat(first_name, " ", last_name) as CustomerName, 
   address, 
   COALESCE(address2,'None Provided') as address2, 
   postal_code 
from customer
inner join address 
using (address_id);

如果数据包含空字符串或 null，那么我会考虑使用:

select concat(first_name, " ", last_name) as CustomerName, 
   address, 
   case 
     when address2 is null or address2 = '' 
     then 'None Provided' 
     else address2 end as address2, 
   postal_code 
from customer
inner join address 
using (address_id);