DUAL table - Oracle Database Full Tutorial

Oracle Database - DUAL table

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The following example returns the current operating system date and time `select sysdate from dual`
The following example generates numbers between start_value and end_value `select :start_value + level -1 n from dual connect by level <= :end_value - :start_value + 1` Remarks `DUAL` table has one column `DUMMY`, defined to be `VARCHAR2(1)` and only one row with a value `x`. `DUAL` table is automatically created in `SYS` schema when database is created. You can access it from any schema. You can not change `DUAL` table. You can use `DUAL` table to call any function from SQL statement. It is useful because it has only one row and oracle optimizer knows everything about it.

The following example returns the current operating system date and time

select sysdate from dual

The following example generates numbers between start_value and end_value

select :start_value + level -1 n
from dual       
connect by level <= :end_value  - :start_value + 1

Remarks

DUAL table has one column DUMMY, defined to be VARCHAR2(1) and only one row with a value x.

DUAL table is automatically created in SYS schema when database is created. You can access it from any schema.

You can not change DUAL table.

You can use DUAL table to call any function from SQL statement. It is useful because it has only one row and oracle optimizer knows everything about it.

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