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Pseudo Column

Pseudo columns in SQL are virtual columns automatically created in tables, such as ROWID, which uniquely identifies the physical location of each row. They are essential for managing data, such as deleting duplicates using SELECT DISTINCT combined with ROWID to ensure unique records. The RNUM pseudo column provides a sequential number for result sets, while the LEVEL pseudo column indicates the depth in hierarchical queries, aiding in organizing relationships (e.g., employees). Additionally, derived tables can be created through queries, simplifying access to sequential or hierarchical data for better analysis.