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…rect results A descending scan of a partitioned table through a secondary index can stop early and omit qualifying rows. ha_partition::handle_unordered_prev() validates the unordered prefix with key number 0 instead of the active index. If the secondary index has a different layout from the primary key, that comparison can incorrectly signal end of file. Pass active_index to key_cmp_if_same() so the prefix comparison uses the index that produced the current row. The regression scans a RANGE-partitioned table using a secondary (b,c) index and checks that ORDER BY c DESC returns all three values: 15, 11, and 6. Bug report: https://jira.mariadb.org/browse/MDEV-40479
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A descending scan of a partitioned table through a secondary index can stop early and omit qualifying rows.
Bug report: https://jira.mariadb.org/browse/MDEV-40479
Root cause
ha_partition::handle_unordered_prev() validates the unordered prefix with key number 0 instead of the active index. If the secondary index has a different layout from the primary key, that comparison can incorrectly signal end of file.
Changes
Regression coverage
The regression scans a RANGE-partitioned table using a secondary (b,c) index and checks that ORDER BY c DESC returns all three values: 15, 11, and 6.
mysql-test/main/partition_reverse_prefix_scan.testmysql-test/main/partition_reverse_prefix_scan.resultValidation
On
12.3at881b64e8add374802e1871814dd0a3a673a9b3e6:main.partition_reverse_prefix_scanfailed on the unchanged target branch and passed with this fix.main.select.