Matt Burgess created NIFI-5855:
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Summary: Optimize GenerateTableFetch to remove unnecessary ORDER
BY clause
Key: NIFI-5855
URL: https://issues.apache.org/jira/browse/NIFI-5855
Project: Apache NiFi
Issue Type: Improvement
Components: Extensions
Reporter: Matt Burgess
Related to NIFI-5727, which for the query that GenerateTableFetch uses to get
column/table information removes an unnecessary COUNT(*) clause when Partition
Size = 0, the ORDER BY clause can also be removed. This is because there will
be a single generated query that will fetch all rows that match the filters.
The ORDER BY is necessary during pagination (when Partition Size > 0) so it can
fetch from Row X to Row Y based on the row number, which is only constant if
the column is ordered.
This Jira proposes to remove the ORDER BY clause from the generated query if
Partition Size is set to 0. Note that this can cause the output of the executed
query to not guaranteed to be ordered; it is a possible change in behavior, but
we don't document any guarantees about row ordering anyway. If the user needs
the rows ordered, they can do it with QueryRecord, or they can add the ORDER BY
clause manually via ReplaceText.
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