How to Find the Unique and Duplicate Data in a Table

Ahmed S — Fri, 03 Aug 2012 10:54:00 +0000

How to Find out Unique and Duplicate Data in a Table

If you want to check the data in a table is unique or duplicate.

In Oracle and Ms SQL Server the standard Having clause for SELECT Statement with built in count function which identify the unique data or duplicate data in a table.

SELECT * From EMP

Idx	FirstName	LastName	Salary
1	Frank	Xylo	5000
2	Smith	Fay	10000
3	Smith	Fay	15000
4	John	Lay	12000
5	John	Fay	14000
6	Ebrahim	John	9000
7	Frank	Xylo	11000
8	Frank	Xylo	7000

This query finds the unique data in a table
SELECT Lastname, count(*)

From EMP

Where lastname = ‘John’

Group By Lastname

Having count(*) = 1;

LasteName	*Count()**
John	1

This query finds the duplicate data in a table

SELECT Lastname, count(*)

From EMP

Where lastname = ‘Fay’

Group By Lastname

Having count(*) > 1;

LasteName	*Count()**
Fay	3

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