Pseudo columns
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. Any SELECT list of columns can include these pseudo columns.
SYSDATE current date and time
ROWNUM sequence number assigned to retrieved rows
ROWID unique identifier for a row
UID number associated with a user
USER userid of current user
The DUAL table
ORACLE provides a "dummy" table called DUAL containing one column and one row. It is useful for selecting miscellaneous information from ORACLE.
Some uses for DUAL
posted on 2006-08-18 08:50
Jcat 阅读(220)
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