使用COALESCE()，这不会连接，但会返回列表中的第一个非空值.

use COALESCE(), this doesn't concatenate but returns the first non-null value from the list.

SELECT Column1, 
       Column2, 
       COALESCE(Column1, Column2) AS Column3 
FROM   TEST_ATTRIBUTES

• SQLFiddle演示
• SQLFiddle Demo

如果它们都有可能为空，

if there are chances that both of them are null,

SELECT Column1, 
       Column2, 
       IF(Column1 IS NULL AND Column2 IS NULL, NULL, CONCAT(COALESCE(Column1,''), COALESCE(Column2,''))) AS Column3 
FROM   TEST_ATTRIBUTES

• SQLFiddle演示
• SQLFiddle Demo