Pseudo Columns in Oracle SQL

Pseudo columns in Oracle SQL are special types of columns that behave like regular columns but are not physically stored in the database. They offer system-level functionality and provide additional capabilities when querying data. Pseudo columns are read-only and are often used for unique system information, data retrieval optimization, or hierarchical data queries. There are several commonly used pseudo columns, including ROWID, LEVEL, SYSDATE, ROWNUM, CURRVAL, NEXTVAL, USER, and CURRENT_USER. Each of these pseudo columns has its own definition and use case, such as ROWID being used for fast data access and LEVEL being used for hierarchical queries. Pseudo columns can be used for performance optimization, hierarchical queries, system data, and unique identifiers. However, they also have limitations, such as being immutable and not being part of the physical schema. When discussing pseudo columns in an interview, it's essential to focus on their practical applications, behavior, and how they are used in Oracle SQL. By highlighting real-world scenarios and discussing performance considerations, hierarchical queries, and example use cases, you can demonstrate both technical understanding and practical knowledge of pseudo columns.