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:
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:
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原文地址:http://blog.csdn.net/xyw_blog/article/details/26250331