How Oracle Silently Handles Duplicate Keys During Unique Index Updates

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Oracle Database allows multi-row updates on unique columns without raising constraint errors, a behavior not shared by databases like PostgreSQL, MySQL, SQLite, and MongoDB. A developer investigated Oracle's internal handling by creating a table with a unique index and a row-level trigger to pause execution between row updates. The experiment revealed that Oracle does not process unique index updates in a straightforward row-by-row manner that would trigger duplicate key violations mid-statement. By dumping index leaf blocks during execution, the researcher aimed to observe how Oracle manages temporary duplicate states within a single update statement. The findings shed light on how Oracle's B-tree index mechanics differ from other databases when enforcing uniqueness constraints during set-based operations.

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