How to Efficiently Copy Rows from One Table to Another While Preventing Duplicates?

Copying Rows with Duplicate Handling in Identical Schema Tables

You want to transfer rows from table 'srcTable' to 'destTable' while preventing duplicates. However, using a subquery in a WHERE clause hasn't worked effectively for you.

Resolving the Issue with WHERE Clauses

The error lies in the absence of a proper clause in the subquery to identify duplicates. Add the necessary conditions in your subquery as follows:

INSERT INTO destTable
SELECT Field1, Field2, Field3, ...
FROM srcTable
WHERE NOT EXISTS(SELECT *
                 FROM destTable
                 WHERE (srcTable.Field1 = destTable.Field1
                       AND srcTable.Field2 = destTable.Field2
                       ... etc.)
                 )

Alternative Approach Using Outer Join

Alternatively, consider using an outer join for a more concise solution:

INSERT INTO destTable
SELECT s.field1, s.field2, s.field3, ...
FROM srcTable s 
       LEFT JOIN destTable d ON (d.Key1 = s.Key1 AND d.Key2 = s.Key2 AND...)
WHERE d.Key1 IS NULL

Handling Duplicates in the Source Table

If your concern lies specifically with duplicate rows in the source table, consider using a distinct clause in your insert statement:

INSERT INTO destTable
SELECT Distinct field1, field2, field3, ...
FROM srcTable  

Additional Recommendations

• Include specific field names in your insert statement instead of using SELECT *.
• Consider using appropriate indexing for optimal performance.

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