Yesterday a friend came across an oracle query problem:
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Consider below table:
Removing duplicate rows from Oracle tables with SQL can be very tricky, and there are several techniques for identifying and removing duplicate rows from tables: Delete multiple duplicate rows Subquery to identify duplicate rows Use RANK to find and remove duplicate table rows. Summary: in this tutorial, you will learn step by step how to delete duplicate records in Oracle Database using the DELETE statement with a subquery. Once you’ve found the duplicate records in a table, you often want to delete the unwanted copies to keep your data clean. If a table has a few duplicate rows, you could do this manually one by one by using a simple DELETE statement.
cid cname.... cdata
1 x xxxx
1 x xxxx ..
2 xzzz fjnd
3 a evddd
Now the problem was cid is repeated and cdata column is having some extra characters but data is considered same (eg. xxxx & xxxx..).
so when he does
He kept on getting duplicated records which intern he wanted to have only one per duplicated cid.
It’s not by the way of table structure but by the way of query he wanted to have results.
so when he does
SELECT cid,cname....cdata FROM TABLENAME ....;
He kept on getting duplicated records which intern he wanted to have only one per duplicated cid.
It’s not by the way of table structure but by the way of query he wanted to have results.
I suggested him:
As far as I know this works with MySQL, but it gave error as I came to know that I have to include all SELECTed variables in GROUP BY clause.
This is Oracle ?
SELECT cid,cname....cdata FROM TABLENAME GROUP BY cid;
As far as I know this works with MySQL, but it gave error as I came to know that I have to include all SELECTed variables in GROUP BY clause.
This is Oracle ?
Well later I came back to my place and recollected something called ROWID of Oracle, may be that can help!!
Oracle Sql Duplicate Rows Query
Then I created similar table in MySQL to “stimulate” Oracle rowID:
rowId cid cname .... cdata
1 1 x xxxx
2 1 x xxxx ..
3 2 xzzz fjnd
4 3 a evddd
And finally I got the solution as:
select cid,cname….cdata from tablename where rowID in (select min(rowID) from tablename group by cid);
So finally I decided to give it a try on Oracle and it worked ?
select * from TABLENAME WHERE rowid in (select min(rowid) from TABLENAME group by DUPLICATECOLUMN);
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You are an Oracle DBA or developer and want to determine the location of duplicate rows in an Oracle table. You need it for example before attempting to place a unique index on the table. See below how can this be done.
Oracle tables always have one guaranteed unique column, the rowid column. If you use a min/max function against your rowid and then select against the proposed primary key you can squeeze out the rowids of the duplicate rows pretty quick. For example:
Find Duplicates In Oracle Table
SELECT * FROM customers o
WHERE rowid > (SELECT min(rowid) FROM customers i
WHERE o.city = i.city and o.rating = i.rating)
WHERE rowid > (SELECT min(rowid) FROM customers i
WHERE o.city = i.city and o.rating = i.rating)
In the situation where multiple columns make up the proposed key,
they must all be used in the WHERE clause.
they must all be used in the WHERE clause.
Here is another simple and dirty way to accomplish the same:
SELECT city, rating, count(*)
FROM customers
GROUP BY city, rating
HAVING count(*) > 1
FROM customers
GROUP BY city, rating
HAVING count(*) > 1
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