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                        /与MySQL的零距离接触

为什么t1.goods_id大于t2.goods_id就能删除两个id大的了?

根据老师的删除代码可以得出查询语句如下

select t1.goods_name,t1.goods_id,t2.goods_name as goods1_name from tdb_goods as t1 LEFT JOIN (SELECT goods_id,goods_name from tdb_goods GROUP BY goods_name HAVING COUNT(goods_id)>=2) as t2 ON t1.goods_name=t2.goods_name where t1.goods_id>t2.goods_id,结果如下,确实是两条记录:

当我去掉WHERE条件后,即:

select t1.goods_name,t1.goods_id,t2.goods_name as goods1_name,t2.goods_id as goods1_id from tdb_goods as t1 LEFT JOIN (SELECT goods_id,goods_name from tdb_goods GROUP BY goods_name HAVING COUNT(goods_id)>=2) as t2 ON t1.goods_name=t2.goods_name;