ORACLE 删除重复的数据

--查询出所有有重复的数据
select DETAIL_ID,COMMENT_BODY,count(*)
from BBSCOMMENT
group by DETAIL_ID,COMMENT_BODY
having count(*)>1
order by DETAIL_ID, COMMENT_BODY; --1955条

2.2 显示了所有的非冗余的数据

--这一条命令显示了所有的非冗余的数据
select min(COMMENT_ID) as COMMENT_ID,DETAIL_ID,COMMENT_BODY
from BBSCOMMENT
group by DETAIL_ID,COMMENT_BODY;   --21453条，之所以此值不等于表总记录数-1955，是因为1955条记录中，有的重复了不止一次。

2.3 如果记录数量少（千级别），可以把上面的语句做成子查询然后直接删除

--如果表数据量不是很大（1千条以内），可以把上面的语句做成子查询然后直接删除
delete from BBSCOMMENT where COMMENT_ID not in(
    select min(COMMENT_ID)
    from BBSCOMMENT
    group by DETAIL_ID,COMMENT_BODY
);          --782秒，在我这里，2万条记录，重复记录2千多（太慢了！！）

2.4 另一种删除方法

--这条语句也能够实现上述功能，但不好测试了，数据已经被我删除了
--删除条件一：有重复数据的记录；条件二：保留最小rowid的记录。
delete from BBSCOMMENT a
where
    (a.DETAIL_ID,a.COMMENT_BODY) in(select DETAIL_ID,COMMENT_BODY from BBSCOMMENT group by DETAIL_ID,COMMENT_BODY having count(*) > 1)
    and rowid not in (select min(rowid) from BBSCOMMENT group by DETAIL_ID,COMMENT_BODY having count(*)>1);

2.5 大数据量还是用PL/SQL方便快捷

declare
--定义存储结构
type bbscomment_type is record
(
    comment_id BBSCOMMENT.COMMENT_ID%type,
    detail_id BBSCOMMENT.DETAIL_ID%type,
    comment_body BBSCOMMENT.COMMENT_BODY%type
);
bbscomment_record bbscomment_type;

--可供比较的变量
v_comment_id BBSCOMMENT.COMMENT_ID%type;
v_detail_id BBSCOMMENT.DETAIL_ID%type;
v_comment_body BBSCOMMENT.COMMENT_BODY%type;

--其它变量
v_batch_size integer := 5000;
v_counter integer := 0;

cursor cur_dupl is
    --取出所有有重复的记录
    select COMMENT_ID, DETAIL_ID, COMMENT_BODY
    from BBSCOMMENT
    where(DETAIL_ID, COMMENT_BODY) in (
        --这些记录有重复
        select DETAIL_ID, COMMENT_BODY
        from BBSCOMMENT
        group by DETAIL_ID, COMMENT_BODY
        having count(*) > 1)
    order by DETAIL_ID, COMMENT_BODY;
begin
    for bbscomment_record in cur_dupl loop
        if v_detail_id is null or (bbscomment_record.detail_id != v_detail_id or nvl(bbscomment_record.comment_body, ‘ ‘) != nvl(v_comment_body, ‘ ‘)) then
            --首次进入、换记录了，都重新赋值
            v_detail_id := bbscomment_record.detail_id;
            v_comment_body := bbscomment_record.comment_body;
        else
            --其它记录删除
            delete from BBSCOMMENT where COMMENT_ID = bbscomment_record.comment_id;
            v_counter := v_counter + 1;

            if mod(v_counter, v_batch_size) = 0 then
                --每多少条提交一次
                commit;
            end if;
        end if;
    end loop;

    if v_counter > 0 then
        --最后一次提交
        commit;
    end if;

    dbms_output.put_line(to_char(v_counter)||‘条记录被删除！‘);
exception
    when others then
        dbms_output.put_line(‘sqlerrm-->‘ ||sqlerrm);
        rollback;
end;

ORACLE 删除重复的数据

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