mysql一关联查询

##mysql一关联查询，很有用的，可以查找到手机号码所在的城市。
select LEFT (a.mobile,7) as mobile,b.city from tb_tvc_mobile a, tb_area_phone_temp b where LEFT (a.mobile,7)=b.code;

select a.*,LEFT (a.mobile,7) as mobile,b.city from tb_tvc_mobile a left join tb_area_phone_temp b
on LEFT (a.mobile,7)=b.code where 1;