在本例中所用数据表结构如下所示tdb_goods
表中数据重复如图所示
首先第一步，利用group by分组查出每组中数目大于2的（即重复记录的）内容
mysql> SELECT goods_id,goods_name FROM tdb_goods GROUP BY goods_name HAVING COUN T(goods_name)>=2; +----------+------------------------------+ | goods_id | goods_name | +----------+------------------------------+ | 20 | X3250 M4机架式服务器 2583i14 | | 19 | 商务双肩背包 | +----------+------------------------------+ 2 rows in set (0.01 sec)
然后使用LEFT JOIN使原始表和上述查询结果进行连接，删除重复记录，保留id较小的记录
mysql> DELETE t1 FROM tdb_goods AS t1 LEFT JOIN( SELECT goods_id,goods_name FROM tdb_goods GROUP BY goods_name HAVING COUNT(goods_name)>=2) AS t2 ON t1.goods_na me = t2.goods_name WHERE t1.goods_id>t2.goods_id; Query OK, 2 rows affected (0.06 sec)
从上述语句可以看出，条件是名称相同的，然后删除所有goods_id大的记录。这样就可以实现想要的效果。
如果想保留id较大的同理，如下所示
mysql> DELETE t1 FROM tdb_goods AS t1 LEFT JOIN( SELECT max(goods_id) AS goods_i d,goods_name FROM tdb_goods GROUP BY goods_name HAVING COUNT(goods_name)>=2) AS t2 ON t1.goods_name = t2.goods_name WHERE t1.goods_id<t2.goods_id; Query OK, 2 rows affected (0.03 sec)
注关于表连接，如有疑问请查看JOIN的用法。
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