update同一张表的例子

场景： 业务中台--的bd_area表需要把pk_parent（父id）字段更新 解决sql： -- 二级更新 update bd_area a LEFT JOIN (select b.id,substr(b.area_code,1,2) as bcode,substr(b.tree_code,1,3) as btcode from bd_area b where LENGTH(b.tree_co

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