MySQL：如何根据另一列为空，从另一列中选择具有值的列？

Question

I have a query that looks like this:

SELECT id, description, default_error, custom_error  FROM  `table1`;

Which gives me

(int) (Text)       (Varchar)          (Varchar)
id    Description  Default_Error      custom_error
---------------------------------------------------
 1    Hello        Error 123            
 2    World        Error 456          This is a custom Error

I'd like to select an extra column ("error") that has the value of default_error if custom_error is EMPTY, and the value of custom_error if custom_error is NOT EMPTY.

Any idea how to do this in MySQL?

Answer 1

如果custom_error为空，则为空，则可以使用以下命令：

select id, description, coalesce(custom_error, default_error)

Answer 2

Try

SELECT id, description, default_error, custom_error,
  IF(custom_error='', default_error, custom_error) as error
FROM  `table1`;

OR - if custom_error is NULL by default

SELECT id, description, default_error, custom_error,
  ISNULL(custom_error, default_error) as error
FROM  `table1`;

Answer 3

SELECT id, description, default_error, custom_error,
  IF(custom_error='', default_error, custom_error) as error
FROM  `table1`;