mysql重复记录删除，保留一条数据

背景：这是一张品牌表，品牌和城市确定是一条数据。
脚本思路：1.根据品牌名和城市进行分组查询出来重复的品牌名，2.再查询出来重复数据的最小id。3.删除这些品牌名但是不包括2查询出来的id。

sql脚本1：

DELETE 
FROM
    dw_brand_expand 
WHERE
    brand_name IN (SELECT brand_name FROM dw_brand_expand GROUP BY brand_name, city_name HAVING COUNT( * ) > 1) 
    AND id NOT IN (SELECT min( id ) FROM dw_brand_expand GROUP BY brand_name, city_name HAVING count( * ) > 1)

执行结果1.png

报错了，报错信息如上图，意思是:不能在FROM子句中指定更新的目标表。解决方案：嵌套一层，取个别名，如下。

sql脚本2：

DELETE 
FROM
    dw_brand_expand 
WHERE id in
(select id from (select id from dw_brand_expand where 
    brand_name IN (SELECT brand_name FROM dw_brand_expand GROUP BY brand_name, city_name HAVING COUNT( * ) > 1) 
    AND id NOT IN (SELECT min( id ) FROM dw_brand_expand GROUP BY brand_name, city_name HAVING count( * ) > 1)) as tmpresult)

执行结果2.png

执行成功，0行是因为执行过一次了，起到显示作用即可。