How do I find duplicate values in a table in Oracle?

What's the simplest SQL statement that will return the duplicate values for a given column and the count of their occurrences in an Oracle database table?

For example: I have a JOBS table with the column JOB_NUMBER. How can I find out if I have any duplicate JOB_NUMBERs, and how many times they're duplicated?

1

13 Answers

Aggregate the column by COUNT, then use a HAVING clause to find values that appear greater than one time.

SELECT column_name, COUNT(column_name)
FROM table_name
GROUP BY column_name
HAVING COUNT(column_name) > 1;

6

Another way:

SELECT *
FROM TABLE A
WHERE EXISTS ( SELECT 1 FROM TABLE WHERE COLUMN_NAME = A.COLUMN_NAME AND ROWID < A.ROWID
)

Works fine (quick enough) when there is index on column_name. And it's better way to delete or update duplicate rows.

3

Simplest I can think of:

select job_number, count(*)
from jobs
group by job_number
having count(*) > 1;

4

You don't need to even have the count in the returned columns if you don't need to know the actual number of duplicates. e.g.

SELECT column_name
FROM table
GROUP BY column_name
HAVING COUNT(*) > 1

How about:

SELECT <column>, count(*)
FROM <table>
GROUP BY <column> HAVING COUNT(*) > 1;

To answer the example above, it would look like:

SELECT job_number, count(*)
FROM jobs
GROUP BY job_number HAVING COUNT(*) > 1;

In case where multiple columns identify unique row (e.g relations table ) there you can use following

Use row id e.g. emp_dept(empid, deptid, startdate, enddate) suppose empid and deptid are unique and identify row in that case

select oed.empid, count(oed.empid)
from emp_dept oed
where exists ( select * from emp_dept ied where oed.rowid <> ied.rowid and ied.empid = oed.empid and ied.deptid = oed.deptid ) group by oed.empid having count(oed.empid) > 1 order by count(oed.empid);

and if such table has primary key then use primary key instead of rowid, e.g id is pk then

select oed.empid, count(oed.empid)
from emp_dept oed
where exists ( select * from emp_dept ied where oed.id <> ied.id and ied.empid = oed.empid and ied.deptid = oed.deptid ) group by oed.empid having count(oed.empid) > 1 order by count(oed.empid);

0

Doing

select count(j1.job_number), j1.job_number, j1.id, j2.id
from jobs j1 join jobs j2 on (j1.job_numer = j2.job_number)
where j1.id != j2.id
group by j1.job_number

will give you the duplicated rows' ids.

SELECT SocialSecurity_Number, Count(*) no_of_rows
FROM SocialSecurity
GROUP BY SocialSecurity_Number
HAVING Count(*) > 1
Order by Count(*) desc 

I usually use Oracle Analytic function ROW_NUMBER().

Say you want to check the duplicates you have regarding a unique index or primary key built on columns (c1, c2, c3). Then you will go this way, bringing up ROWID s of rows where the number of lines brought by ROW_NUMBER() is >1:

Select *
From Table_With_Duplicates
Where Rowid In (Select Rowid From (Select ROW_NUMBER() Over ( Partition By c1, c2, c3 Order By c1, c2, c3 ) nbLines From Table_With_Duplicates) t2 Where nbLines > 1)

I know its an old thread but this may help some one.

If you need to print other columns of the table while checking for duplicate use below:

select * from table where column_name in
(select ing.column_name from table ing group by ing.column_name having count(*) > 1)
order by column_name desc;

also can add some additional filters in the where clause if needed.

Here is an SQL request to do that:

select column_name, count(1)
from table
group by column_name
having count (column_name) > 1;

1. solution

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

1

Also u can try something like this to list all duplicate values in a table say reqitem

SELECT count(poid)
FROM poitem
WHERE poid = 50
AND rownum < any (SELECT count(*) FROM poitem WHERE poid = 50)
GROUP BY poid
MINUS
SELECT count(poid)
FROM poitem
WHERE poid in (50)
GROUP BY poid
HAVING count(poid) > 1;