How to print duplicate rows in a table?

Let us consider below table.

Name	Section
abc	CS1
bcd	CS2
abc	CS1

In the above table, we can find duplicate row using below query.

SELECT name, section FROM tbl
GROUP BY name, section
HAVING COUNT(*) > 1

Another Example:
Given a table named PERSON task is to write an SQL query to find all duplicate name in the table.
Example :

+----+---------+
| Id | NAME    |
+----+---------+
| 1  | Geeks   |
| 2  | for     |
| 3  | Geeks   |
+----+---------+

Output :
+---------+
| NAME    |
+---------+
| Geeks   |
+---------+

The simple approach is to make a temporary table which have count of all the names in a table.

Duplicated NAME existed more than one time, so to count the times each NAME exists, we can use the following code:

select NAME, count(NAME) as num
from Person
group by NAME;

| NAME    | num |
|---------|-----|
| Geeks   | 2   |
| for     | 1   |

This is a temporary table, on which we can run the below code to get duplicate NAME.

select NAME from
(
  select NAME, count(NAME) as num
  from Person
  group by NAME
) as statistic
where num > 1;

The Best approach is to use GROUP BY and HAVING condition. It is more effective and faster then previous.

MySql :

select NAME
from Person
group by NAME
having count(NAME) > 1;

This article is contributed by Sahil Rajput. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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Last Updated : 21 Jun, 2018

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