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PostPosted: Mon Nov 07, 2016 6:50 am 
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Joined: Fri Nov 13, 2015 3:56 am
Posts: 460
A pseudocolumn behaves like a table column, but is not actually stored in the table. You can select from pseudocolumns, but you cannot insert, update, or delete their values.

Pseudocolumns are virtual columns that are available in special cases. In an Oracle database, there's a ROWNUM pseudocolumn that will give you the row number.

SQL server, as far as I know, doesn't actually support pseudocolumns but there are errors and stored procedures that refer to pseudo columns, probably for Oracle migration.

Some more examples of pseudo columns are
1.SYSDATE;
2.ROWNUM;
3.ROWID;
4.NEXTVAL;
5.CURRVAL;
6.LEVEL;

They can also be called hidden columns, particularly if they are (contrary to pseudo-columns) actually stored in the database, but are not selected by *; you have to specifically request the column to see it.

A pseudo column is an item of data which does not belong in any particular table but which can be treated as if it did.Pseudo columns behave like a table column, but it is not actually stored in a table.

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PostPosted: Tue Dec 13, 2016 12:37 pm 
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Joined: Wed Jul 01, 2015 11:28 am
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A pseudo-column is an Oracle assigned value (pseudo-field) but not stored on disk. Pseudocolumns are not actual columns in a table but they behave like columns. For example, you can select values from a pseudocolumn. SQL> SELECT sysdate, systimestamp FROM dual; SYSDATE SYSTIMESTAMP.

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