How to Delete Duplicate Rows in SQL Without a Unique Identifier?

Remove duplicate rows without unique identifier

To remove duplicate rows from a table that do not have a unique identifier column, you can use a CTE (common table expression) in conjunction with ROW_NUMBER().

Solution:

Please consider the following inquiry:

<code class="language-sql">WITH CTE AS (
   SELECT [col1], [col2], [col3], [col4], [col5], [col6], [col7],
       RN = ROW_NUMBER() OVER (PARTITION BY col1 ORDER BY col1)
   FROM dbo.Table1
)
DELETE FROM CTE WHERE RN > 1;</code>

This query does the following:

1. Create CTE: It creates a CTE named "CTE", assigns each row a unique ROW_NUMBER(), counting starting from 1 of the "col1" column in each unique value partition .
2. Identify duplicates: The query identifies duplicate rows by checking if ROW_NUMBER() is greater than 1.
3. Remove Duplicates: It then removes all rows in the CTE that have duplicate ROW_NUMBER() values.

Result:

The result of the query is a table with duplicate rows removed, retaining only the first occurrence of each unique row. This is achieved without requiring a unique identifier column in the original table.

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