1.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：

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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：假设region_name一列的值为空，则显示为0，结果为：

本文为Eliot原创，转载请注明出处：http://blog.csdn.net/xyw_blog/article/details/26250331