It is suitable for use in selecting a pseudocolumn such as SYSDATE or USER. The table has a single VARCHAR2(1) column called DUMMY that has a value of 'X'.
DUALis a table automatically created by Oracle Database along with the data dictionary.
DUALis in the schema of the user
SYSbut is accessible by the name
DUALto all users. It has one column,
DUMMY, defined to be
VARCHAR2(1), and contains one row with a value
X. Selecting from the
DUALtable is useful for computing a constant expression with the
DUALhas only one row, the constant is returned only once. Alternatively, you can select a constant, pseudocolumn, or expression from any table, but the value will be returned as many times as there are rows in the table. Please refer to "SQL Functions" for many examples of selecting a constant value from
SELECT 1+1 FROM DUAL;
SELECT USER FROM DUAL;