##121.308364,30.225778 示例对比的坐标select * from broadcasts where location!='' and sqrt( ( ((121.308364-longitude)*PI()*12656*cos(((30.225778+latitude)/2)*PI()/180)/180) * ((121.308364-longitude)*PI()*12656*cos (((30.225778+latitude)/2)*PI()/180)/180) ) + ( ((30.225778-latitude)*PI()*12656/180) * ((30.225778-latitude)*PI()*12656/180) ) )<20