mysql去除重复数据，只保留一条。

之前写过的爬虫里面，因为种种原因出现了一些重复的数据需要删除掉。然后发现mysql并没有直接的去重功能，要自己写。

查过许多博客之后发现可以这么写。

删除ppeople 重复的数据，然后重复数据中保留id最小的那一条数据。

delete from people 
where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1) 
and rowid not in (select min(rowid) from people group by peopleId having count(peopleId )>1) 

但是执行之后发现mysql不支持这么写。报错信息为：

You can't specify target table 'news' for update in FROM clause

查阅之后发现，应当把查询结果通过中间表再查询一遍才行。

修改为：

deletefrom news

wherenewsurl in (select NewsUrl from (select NewsUrl from news group by newsurlhaving count(newsurl) > 1) a)


andnewsid not in ( select newsid from (select min(newsid) as newsid  from news group by newsurl havingcount(newsurl )>1) b)

运行成功