Removing duplicate rows from table in Oracle

Question

I\'m testing something in Oracle and populated a table with some sample data, but in the process I accidentally loaded duplicate records, so now I can\'t create a primary ke

Answer 1

You should do a small pl/sql block using a cursor for loop and delete the rows you don't want to keep. For instance:

declare
prev_var my_table.var1%TYPE;

begin

for t in (select var1 from my_table order by var 1) LOOP

-- if previous var equal current var, delete the row, else keep on going.
end loop;

end;

Answer 2

DELETE from table_name where rowid not in (select min(rowid) FROM table_name group by column_name);

and you can also delete duplicate records in another way

DELETE from table_name a where rowid > (select min(rowid) FROM table_name b where a.column=b.column);

Answer 3

Solution 4)

 delete from emp where rowid in
            (
             select rid from
                (
                  select rowid rid,
                  dense_rank() over(partition by empno order by rowid
                ) rn
             from emp
            )
 where rn > 1
);

Answer 4

From DevX.com:

DELETE FROM our_table
WHERE rowid not in
(SELECT MIN(rowid)
FROM our_table
GROUP BY column1, column2, column3...) ;

Where column1, column2, etc. is the key you want to use.

Answer 5

To select the duplicates only the query format can be:

SELECT GroupFunction(column1), GroupFunction(column2),..., 
COUNT(column1), column1, column2...
FROM our_table
GROUP BY column1, column2, column3...
HAVING COUNT(column1) > 1

So the correct query as per other suggestion is:

DELETE FROM tablename a
      WHERE a.ROWID > ANY (SELECT b.ROWID
                             FROM tablename b
                            WHERE a.fieldname = b.fieldname
                              AND a.fieldname2 = b.fieldname2
                              AND ....so on.. to identify the duplicate rows....)

This query will keep the oldest record in the database for the criteria chosen in the WHERE CLAUSE.

Oracle Certified Associate (2008)

Answer 6

Solution 1)

delete from emp
where rowid not in
(select max(rowid) from emp group by empno);

Solution 2)

delete from emp where rowid in
               (
                 select rid from
                  (
                    select rowid rid,
                      row_number() over(partition by empno order by empno) rn
                      from emp
                  )
                where rn > 1
               );

Solution 3)

delete from emp e1
         where rowid not in
          (select max(rowid) from emp e2
           where e1.empno = e2.empno );