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pouta
V2EX  ›  MySQL

关于数据库去除重复记录,有什么优雅的写法

  •  
  •   pouta · Nov 18, 2016 · 4553 views
    This topic created in 3460 days ago, the information mentioned may be changed or developed.
    delete from demo_user where id in(
    
    //获取重复记录的 id
    select id from demo_user 
    where id > any (select id from demo_user where age in (select age from demo_user group by age having count(age) > 1))
    and id <= some (select id from demo_user where age in (select age from demo_user group by age having count(age) > 1))
    
    );
    

    报了 error: You can't specify target table 'demo_user' for update in FROM clause

    12 replies    2016-11-20 00:33:30 +08:00
    20150517
        1
    20150517  
       Nov 19, 2016   ❤️ 3
    先要删的记录先 insert into xxxx (select xxx from xxxx)
    然后再 delete from xxx where id in (select xxx from xxxx)
    Layne
        2
    Layne  
       Nov 19, 2016
    楼上说的这是流着泪积累的经验,楼主你值得拥有。。
    ihuotui
        3
    ihuotui  
       Nov 19, 2016 via Android
    就是用一个 id 唯一索引的表保存一次,然后改表名,即有备份又得到结果
    dalang
        4
    dalang  
       Nov 19, 2016 via iPhone
    我一般都是先把要操作的 table duplicate 一份
    caomaocao
        5
    caomaocao  
       Nov 19, 2016
    @20150517 老司机经验啊!
    pouta
        6
    pouta  
    OP
       Nov 19, 2016
    @20150517 就是说要删除的记录 先保存下来是吗
    rockpk008
        7
    rockpk008  
       Nov 19, 2016 via iPhone
    一楼绝壁有过故事
    pouta
        8
    pouta  
    OP
       Nov 19, 2016
    @dalang 我现在是学 看各位有没有更好的写法
    lrh3321
        9
    lrh3321  
       Nov 19, 2016
    @pouta 批量删除和改数据前,最好先备份。 至少能保证 SQL 写错了的时候,你可以回档。

    删库跑路并不是说着玩的
    pouta
        10
    pouta  
    OP
       Nov 19, 2016
    @lrh3321 所以各位能不能看下我写的 sql 语句
    20150517
        11
    20150517  
       Nov 20, 2016
    @rockpk008 哈哈,数据工程师多年,泪的教训太多了...不过我说的 insert 是 insert 主键就够了
    20150517
        12
    20150517  
       Nov 20, 2016
    @pouta 你要确定没问题就只保存主键,要是数据重要,量又不大,就先拷一份咯
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