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Asked by Nikhil Last Modified
Answer To delete duplicate rows while keeping one copy in an SQL Server table, you can use a common table expression (CTE) with the ROW_NUMBER() window function to identify and delete duplicates. Here's an example query:
```sql
WITH CTE AS (
SELECT
YourColumns,
ROW_NUMBER() OVER (PARTITION BY Column1, Column2, ... ORDER BY (SELECT NULL)) AS RowNum
FROM YourTable
)
DELETE FROM CTE WHERE RowNum > 1;
```
Replace `YourTable` with the name of your table and `YourColumns` with the actual column names. The `PARTITION BY` clause in the `ROW_NUMBER()` function is used to define the columns based on which you want to identify duplicates. You should list all the columns that, when combined, determine what makes a row a duplicate.
This query will delete all rows except the one with the lowest row number within each set of duplicates. The `ORDER BY (SELECT NULL)` ensures that the `ROW_NUMBER()` is applied without any specific order.
Before running such queries, it's always a good practice to have a backup of your data or to try it on a test environment to ensure it behaves as expected.
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