The Oracle DUAL table

The DUAL table in Oracle database is a technical table with one column named DUMMY (data type VARCHAR2(1)) and one row of data of value 'x' in it. So SELECT * FROM DUAL will give the following result.

DUMMY
-----------
x

The DUAL table is often used to satisfy the SQL syntax that a query must have at least the SELECT and FROM clauses.

For example
SELECT 'My Answer' FROM DUAL;
returns 'My Answer' as the value.

SELECT 'My Answer' || ' Your Answer' FROM DUAL;
returns 'My Answer Your Answer' as the value.

SELECT 1345 FROM DUAL;
returns 1345 as the value.

SELECT 5*20 FROM DUAL;
returns the calculation result (100) as the value. Variance kind of calculations can be performed here.

SELECT SYSDATE FROM DUAL;
returns the current date

SELECT USER FROM DUAL;
returns the user ID that is used to connect to the database.

SELECT <your sequence>.nextval FROM DUAL;
returns the next value from the sequence.

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