使用mysql中的select语句替换sql中的空值?

问题描述：

怎么做?使用 select 语句可以编写什么查询，其中所有空值都应替换为 123?

Ho to do this? What query can be written by using select statement where all nulls should be replaced with 123?

我知道我们可以使用，update tablename set fieldname = "123" where fieldname is null;

I know we can do this y using, update tablename set fieldname = "123" where fieldname is null;

但不能使用 select 语句.

答

在 MySQL 中替换 NULL 值有很多选择:

You have a lot of options for substituting NULL values in MySQL:

select case 
    when fieldname is null then '123' 
    else fieldname end as fieldname 
from tablename

select coalesce(fieldname, '123') as fieldname 
from tablename

select ifnull(fieldname, '123') as fieldname 
from tablename