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Question and Answer

Connor McDonald

Thanks for the question, Nissa.

Asked: October 17, 2017 - 6:02 pm UTC

Last updated: October 24, 2017 - 1:42 am UTC

Version: G

Viewed 1000+ times

You Asked

Hello,

I'd like to remove duplicates from ma table let say V1 is the key column. the key should be max 5 digits as a length

Example:
V1

01254T
50300
50300W
45662

Here I should keep the first one (it has no duplicates) , 50300 and the last one.

I tried this querry but doesn't work

SELECT tab.*
FROM mytable tab
join (
select substr(V1, 1, 5) as tab1, min(length(V1))
FROM tab
group by substr(V1, 1, 5)
) tab1
on substr(corp.V1, 1, 5) = tab1.subb;

Can you help please?

Thank you

Mila






and Connor said...

SQL> create table t ( x varchar2(10));

Table created.

SQL>
SQL> insert into t values ('01254T');

1 row created.

SQL> insert into t values ('50300');

1 row created.

SQL> insert into t values ('50300W');

1 row created.

SQL> insert into t values ('45662');

1 row created.

SQL>
SQL> select x,
  2    count(*) over ( partition by substr(x,1,5)) as c
  3  from t;

X                   C
---------- ----------
01254T              1
45662               1
50300W              2
50300               2

4 rows selected.

SQL>
SQL> select *
  2  from (
  3  select x,
  4    count(*) over ( partition by substr(x,1,5)) as c
  5  from t
  6  )
  7  where c = 1;

X                   C
---------- ----------
01254T              1
45662               1

2 rows selected.


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Comments

plus delete

Racer I., October 18, 2017 - 10:51 am UTC

Hi,

delete from t where rowid NOT IN (
  select min(rowid) keep (dense_rank first order by rowid) row_id
  from t
  group by substr(x,1,5))

or : order by x, rowid
or : order by length(x), rowid


Chris Saxon
October 18, 2017 - 3:07 pm UTC

Yep. But why the need for the keep clause?

Why the keep?

A reader, October 23, 2017 - 12:09 pm UTC

I believe the original poster is trying to keep every first occurrence of substr(V1, 1, 5). He wants the result from his example to be:

01254T
50300
45662

not:

01254T
45662
Connor McDonald
October 24, 2017 - 1:42 am UTC

Fair point - I didnt read that from his question but a KEEP or substituting my "count" with "row_number" will do the trick
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