How to avoid inserting duplicate records when using a T-SQL Merge statement

Question

I am attempting to insert many records using T-SQL\'s MERGE statement, but my query fails to INSERT when there are duplicate records in the source table. The failure is caused b

Answer 1

Instead of GROUP BY you can use an analytic function, allowing you to select a specific record in the set of duplicate records to merge.

MERGE INTO dbo.tbl1 AS tbl
USING (
    SELECT *
    FROM (
        SELECT *, ROW_NUMBER() OVER (PARTITION BY col2, col3 ORDER BY ModifiedDate DESC) AS Rn
        FROM #tmp
    ) t
    WHERE Rn = 1    --choose the most recently modified record
) AS src
ON (tbl.col2 = src.col2 AND tbl.col3 = src.col3)