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?
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; 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.
Simplest I can think of:
select job_number, count(*) from jobs group by job_number having count(*) > 1; 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); 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); 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; 
