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

Solved to your new specification. Only inserting the highest value of col4: This time I used a group by to prevent duplicate rows.

MERGE INTO dbo.tbl1 AS tbl 
USING (SELECT col2,col3, max(col4) col4 FROM #tmp group by col2,col3) AS src 
ON (tbl.col2 = src.col2 AND tbl.col3 = src.col3) 
WHEN NOT MATCHED THEN  
    INSERT (col2,col3,col4) 
    VALUES (src.col2,src.col3,src.col4);