A Pseudocolumn is a "column" that yields a value when selected, but which is not an actual column of the table. An example is RowID or SysDate.
It is often used in combination with the
DUAL table The DUAL table is a special one-row, one-column table present by default in Oracle and other database installations. In Oracle, the table has a single VARCHAR2(1) column called DUMMY that has a value of 'X'. It is suitable for use in selecting a pse ...
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References
Databases
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