快捷導(dǎo)航

oracle數(shù)據(jù)庫去除重復(fù)數(shù)據(jù)常用的方法總結(jié)

更新時(shí)間：2022年05月20日 11:36:07 作者：nayi_224

數(shù)據(jù)清理的時(shí)候常常會(huì)清除表中的重復(fù)的數(shù)據(jù),那么在oracle中怎么處理呢？下面這篇文章主要給大家介紹了關(guān)于oracle數(shù)據(jù)庫去除重復(fù)數(shù)據(jù)常用的方法,需要的朋友可以參考下

創(chuàng)建測試數(shù)據(jù)

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(jié)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?yàn)樗荒軐θ坎樵兊牧凶鋈ブ?。如果我想對col_2,col3去重，那我的結(jié)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(fù)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(huì)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(fù)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(fù)數(shù)據(jù)并保留一條

分析函數(shù)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(shù)一貫的靈活性高的特點(diǎn)?？梢詾樗麨榈姆纸M，并通過改變orderby從句來達(dá)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(jié)

到此這篇關(guān)于oracle數(shù)據(jù)庫去除重復(fù)數(shù)據(jù)常用的文章就介紹到這了,更多相關(guān)oracle去除重復(fù)數(shù)據(jù)內(nèi)容請搜索腳本之家以前的文章或繼續(xù)瀏覽下面的相關(guān)文章希望大家以后多多支持腳本之家！

您可能感興趣的文章: