Question

嗨我有以下表格：

列：word，docNum，频率

示例行：

ana,0,1
bob,1,2
ana,0,3
pen,2,2

我想通过删除重复的行并总结＆＃34;频率＆＃34;来更新我的表格。值。所以输出将是：

ana,0,4
bob,1,2
pen,2,2

我不想使用临时表。你能帮我写一下Mysql查询吗？

Answer 1

您可以使用两个单独的命令update和delete执行此操作：

update table t join
       (select word, docnum, sum(frequency) as freq
        from table t
        group by word, docnum
       ) tsum cross join
       (select @rn := -1) hack
    t.frequency = tsum.freq + (@rn := @rn + 1);

delete t
    from table t
    where not exists (select 1
                      from table t2
                      where t2.word = t.word and
                            t2.docnum = t.docnum and
                            t2.frequency > t.frequency
                     );

update语句将频率设置为每个单词/ docnum对的增加值。 delete然后删除除最小值之外的所有值。

作为一个说明，我永远不会使用这种逻辑。相反，我只会这样做：

create temporary table tsum as
        select word, docnum, sum(frequency) as freq
        from table t
        group by word, docnum;

truncate table t;

insert into t(word, docnum, frequency)
    select word, docnum, freq
    from tsum;

按值对行进行求和，并删除Mysql中的重复行

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