1.在没有设置默认值的情况下：SELECTuserinfo.id,user_name,role,adm_regionid,region_name,create_timeFROMuserin1.在没有设置默认值的情况下：
SELECT userinfo.id, user_name, role, adm_regionid, region_name , create_time
FROM userinfo
LEFT JOIN region ON userinfo.adm_regionid = region.id
结果：
设置显示默认值：
SELECT userinfo.id, user_name, role, adm_regionid, IFNULL(region_name,0) as region_name, create_time
FROM userinfo
LEFT JOIN region ON userinfo.adm_regionid = region.id
即：如果region_name一列的值为空，则显示为0，结果为：
本文来自：http://blog.csdn.net/xyw_blog/article/details/26250331 Mysql select 设置默认值