The DUAL table is automatically created in OceanBase Database along with the data dictionary. The DUAL table is located in the schema of the SYS user, but all users can access it by using the DUAL name.
The DUAL table has a column named DUMMY, which is defined as VARCHAR2(1), and contains a row with a value of X. When you use a SELECT statement to calculate a constant expression, you can select data from the DUAL table. This method is more convenient. Because the DUAL table contains only one row, the constant is returned only once. Alternatively, you can select a constant, a pseudo column, or an expression from any table. However, the value returned will depend on the number of rows in the table.