How Can I Find Duplicate Rows and Their IDs in SQL Server?

Finding Duplicate Rows and Associated IDs in SQL Server

Question:

How can I retrieve duplicate rows from a SQL Server database while also including the IDs associated with each row? Consider a scenario where an "organizations" table contains duplicate rows and users link to these organizations in a separate table. To manually unify these users with the organizations, you wish to identify the duplicate organizations and their respective IDs.

Answer:

To retrieve both duplicate organizations and their IDs:

select o.orgName, oc.dupeCount, o.id
from organizations o
inner join (
    SELECT orgName, COUNT(*) AS dupeCount
    FROM organizations
    GROUP BY orgName
    HAVING COUNT(*) > 1
) oc on o.orgName = oc.orgName  

This query accomplishes the following:

• Executes a subquery to identify duplicate organization names and counts them (dupeCount).
• Performs an inner join between the "organizations" table and the subquery result, using the orgName column as the join condition.

This results in a combined output that includes the orgName, dupeCount, and id for all duplicate organizations in the "organizations" table. This information can then be used to identify and manually unify the duplicate organizations while maintaining the integrity of user links to the correct organizations.

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