Selecting from the DUAL Table
DUAL
is a table automatically created by Oracle Database along with the data dictionary. DUAL
is in the schema of the user SYS
but is accessible by the name DUAL
to all users. It has one column, DUMMY
, defined to be VARCHAR2(1)
, and contains one row with a value X
. Selecting from the DUAL
table is useful for computing a constant expression with the SELECT
statement. Because DUAL
has 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 DUAL
.