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Find Duplicate Records in SQL

Oracle. SQL Server, or Access

by Les Smith

How can I find duplicate records on a field in a database table?  This works in SQL Server, Oracle, or Access.

Quite often I encounter the need to find duplicate rcords in database tables.  This brief article will return a results set of duplicate records.

In order to find duplicate values in a table, use the following SQL.

SIMPLE:
select distinct employee from employees (nolock)
group by employee
having count(employee) > 1
order by employee


Complex:
select employee, firstname, lastname, dob
from employees (nolock)
where employee in
(select employee from employees (nolock)
group by employee
having count(employee)>1)
order by employee