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  • Dual Table

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    Dual table:

    • DUAL table is a dummy table which contains one row and one column and by default it is present in database.It contains a single VARCHAR2(1) column known as DUMMY with a value "X".
    • It can be accessed by all users but the owner of DUAL table is SYS. We can use this table to perform some calculation and we can also display system date.
    • It is used when we are interested in result only.

    We can see the structure of the DUAL table using the following query:

    DESC DUAL; 
    

    Output will be like this:

    Name                 Null?   Type
    --------------------------- ------
    DUMMY                        VARCHAR2(1)
    

    We can see the data of dual table using the following query:

    SELECT * FROM DUAL;  
    

    Output will be like this:

    DUMMY
    ----------
    X
    

    Query to check the system date using dual table:

    SELECT sysdate FROM DUAL ; 
    

    Output will be like this:

    SYSDATE
    ---------
    25-JAN-16
    

    Query to perform some calculation using dual table:

    SELECT 25+10-25*25/25 FROM DUAL;  
    

    Output will be like this:

    25+10-25*25/25
    ---------------------
    10.0000
    

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