区域表:

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1.查询河北省下面所有的市。
select * from areas as shi inner join areas as sheng on shi.pid=sheng.id where sheng.name="河北省";

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2.查询张家口市下面所有的县。
select * from areas as shi inner join areas as xian on shi.id=xian.pid where shi.name="张家口市";

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