How to merge in Oracle when matching IDs are not unique?

2 years ago
Benjamin Taylor
2 minutes

When merging two rows with the same ID in Oracle using the MERGE statement, it may result in non-unique IDs. In such cases, a subquery or self-join can be used to resolve the issue.

Here is an example of using a subquery to solve the issue of matching non-unique IDs.

MERGE INTO target_table t
USING (
    SELECT id, value
    FROM source_table
    WHERE condition
) s
ON (t.id = s.id)
WHEN MATCHED THEN
    UPDATE SET t.value = s.value
WHEN NOT MATCHED THEN
    INSERT (id, value)
    VALUES (s.id, s.value);

In the code above, a subquery is used to return specific IDs and values from the source_table. In the MERGE statement, the ON clause is used to match the ID from the target table with the ID from the subquery, then carry out the corresponding operation based on the match result.

Another solution is to use self-joins. Here is an example of using self-joins to resolve non-unique matching IDs:

MERGE INTO target_table t1
USING source_table t2
ON (t1.id = t2.id)
WHEN MATCHED THEN
    UPDATE SET t1.value = t2.value
WHEN NOT MATCHED THEN
    INSERT (id, value)
    VALUES (t2.id, t2.value);

In the code above, a self-join is used to match the ID of the target table with the ID of the source table, and then perform the corresponding operation based on the match result.

Both subqueries and self-joins can be used to handle situations where IDs are not unique. The choice between the two methods depends on your specific needs and data structure.

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