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oracle數據庫去除重復數據常用的方法總結_oracle

作者：nayi_224 ? 更新時間： 2022-07-17 編程語言

創建測試數據

create table nayi224_180824(col_1 varchar2(10), col_2 varchar2(10), col_3 varchar2(10));
insert into nayi224_180824
select 1, 2, 3 from dual union all
select 1, 2, 3 from dual union all
select 5, 2, 3 from dual union all
select 10, 20, 30 from dual ;
commit;
select*from nayi224_180824;
COL_1 COL_2 COL_3
1 2 3
1 2 3
5 2 3
10 20 30

針對指定列，查出去重后的結果集

distinct

select distinct t1.* from nayi224_180824 t1;
COL_1 COL_2 COL_3
10 20 30
1 2 3
5 2 3

方法局限性很大，因為它只能對全部查詢的列做去重。如果我想對col_2,col3去重，那我的結果集中就只能有col_2,col_3列，而不能有col_1列。

select distinct t1.col_2, col_3 from nayi224_180824 t1
COL_2 COL_3
2 3
20 30

不過它也是最簡單易懂的寫法。

row_number()

select *
  from (select t1.*,
               row_number() over(partition by t1.col_2, t1.col_3 order by 1) rn
          from nayi224_180824 t1) t1
 where t1.rn = 1
;
COL_1 COL_2 COL_3 RN
1 2 3 1
10 20 30 1

寫法上要麻煩不少，但是有更大的靈活性。

針對指定列，查出所有重復的行

count having

select *
  from nayi224_180824 t
 where (t.col_2, t.col_3) in (select t1.col_2, t1.col_3
                                from nayi224_180824 t1
                               group by t1.col_2, t1.col_3
                              having count(1) > 1)
COL_1 COL_2 COL_3
1 2 3
1 2 3
5 2 3

要查兩次表，效率會比較低。不推薦。

count over

select *
  from (select t1.*,
               count(1) over(partition by t1.col_2, t1.col_3) rn
          from nayi224_180824 t1) t1
 where t1.rn > 1
;
COL_1 COL_2 COL_3 RN
1 2 3 3
1 2 3 3
5 2 3 3

只需要查一次表，推薦。

刪除所有重復的行

delete from nayi224_180824 t
 where t.rowid in (
                   select rid
                     from (select t1.rowid rid,
                                   count(1) over(partition by t1.col_2, t1.col_3) rn
                              from nayi224_180824 t1) t1
                    where t1.rn > 1);

就是上面的語句稍作修改。

刪除重復數據并保留一條

分析函數法

delete from nayi224_180824 t
 where t.rowid in (select rid
                     from (select t1.rowid rid,
                                  row_number() over(partition by t1.col_2, t1.col_3 order by 1) rn
                             from nayi224_180824 t1) t1
                    where t1.rn > 1);

擁有分析函數一貫的靈活性高的特點。可以為所欲為的分組，并通過改變orderby從句來達到像”保留最大id“這樣的要求。

group by

delete from nayi224_180824 t
 where t.rowid not in
       (select max(rowid) from nayi224_180824 t1 group by t1.col_2, t1.col_3);

犧牲了一部分靈活性，換來了更高的效率。

總結

原文鏈接：https://blog.csdn.net/nayi_224/article/details/82020913

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