Mysqlselect语句设置默认值_MySQL

1.在没有设置默认值的情况下：

SELECT userinfo.id, user_name, role, adm_regionid, region_name , create_timeFROM userinfoLEFT 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_timeFROM userinfoLEFT 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：