MySQL学习笔记（21）——多表删除

多表删除

语法结构：

DELETE tb_name[.*] [,tb_name[.*]] ...
FROM table_references
[WHERE where_condition]

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查出商品名称相同的goods_name:

SELECT goods_id,goods_name FROM tdb_goods GROUP BY goods_name HAVING COUNT(goods_name)>=2;

利用多表删除和子查询删除名字重复的纪录:

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_name = t2.goods_name WHERE t1.goods_id > t2.goods_id;

如图:

使用SELECT * FROM tdb_goods;可以看到id的值只剩下20个，，删除了两个id值比较大的重复商品。