Zoltán Borók-Nagy created IMPALA-12588:
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Summary: Don't update rows that already have the desired value
Key: IMPALA-12588
URL: https://issues.apache.org/jira/browse/IMPALA-12588
Project: IMPALA
Issue Type: Bug
Components: Frontend
Reporter: Zoltán Borók-Nagy
When UPDATEing an Iceberg table, we should write as few new data records and
delete records as possible.
Therefore, if rows already have the new values we should just ignore them.
One way to achieve this is to add extra predicates, e.g.:
{noformat}
UPDATE tbl SET k = 3 WHERE i > 4;
==>
UPDATE tbl SET k = 3 WHERE i > 4 AND k != 3;
{noformat}
So we won't write new data/delete records for the rows that already have the
desired value.
For some cases in can be trickier (e.g. UPDATE FROM), those cases could be
handled more easily by the new MERGE statement when we have it.
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