When migrating from Oracle to KingbaseES (KES), one of the most dangerous yet subtle issues is the difference in how the query optimizer handles outer joins. In Oracle, certain outer join patterns are preserved to guarantee correct results, but KES's optimizer may eliminate them, treating them as inner joins. This can silently drop rows that should have been included, leading to data corruption without any error. The article provides a concrete example and explains how to detect such cases by analyzing query plans. For any team involved in database migration, especially from Oracle to domestic alternatives, understanding this class of semantic mismatch is critical. The recommended approach is to validate migration results with row-count comparisons and plan analysis, not just functional testing.
A deep dive into how outer join elimination during Oracle-to-KingbaseES migration can cause silent data loss, with detection strategies.