How to remove duplicate data in oracle
Oracle method to remove duplicate data: 1. Find all duplicate rows for the specified column and delete them. The method is count having; 2. Delete all duplicate rows. The code is [delete from nayi224_180824 t where t.rowid in].
#The operating environment of this article: Windows7 system, oracle9i version, Dell G3 computer.
Recommended (free): oracle database
oracle removes duplicate data Method:
Create test data
create table nayi224_180824(col_1 varchar2(10), col_2 varchar2(10), col_3 varchar2(10)); insert into nayi224_180824select 1, 2, 3 from dual union allselect 1, 2, 3 from dual union allselect 5, 2, 3 from dual union allselect 10, 20, 30 from dual ;commit;select*from nayi224_180824;
| COL_2 | COL_3 | |
|---|---|---|
| 2 | 3 | |
| 2 | 3 | |
| 2 | 3 | |
| 20 | 30 |
distinct
select distinct t1.* from nayi224_180824 t1;
| COL_3 | ||
|---|---|---|
| 30 | ##1 | |
| 3 | 5 | |
| 3 | The method has great limitations. Because it can only deduplicate all query columns. If I want to deduplicate col_2 and col3, then my result set can only have col_2 and col_3 columns, but not col_1. |
| ##2 | |
|---|---|
| 20 | 30 |
| But it is also the simplest and easiest way to understand. |
COL_1
| RN | 1 | ||
|---|---|---|---|
| 1 | 10 | 20 | |
| 1 | ##It’s a lot more troublesome to write, but it has greater flexibility . |
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| ##1 | 2 | |
|---|---|---|
| 1 | 2 | 3 |
| ##5 | 2 | 3 |
| #The table needs to be checked twice, so the efficiency will be relatively low. Not recommended. | count over |
COL_2
COL_3| ##1 | 2 | 3 | |
|---|---|---|---|
| 1 | 2 | 3 | 3 |
| ##5 | 2 | 3 | 3 |
| You only need to check the table once, recommended. | Delete all duplicate rows | 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); Copy after login | is a slight modification of the above statement.
Analytical function method
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);Has the consistent high flexibility of analytical functions . You can do whatever you want with the grouping and change the orderby clause to achieve requirements like "retain the maximum id".
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);Sacrifice some flexibility in exchange for higher efficiency.
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