Question

1. What is the DUAL table?

2. Explain the USER function.

3. Explain the ROWNUM pseudocolumn.

4. What is a sequence?

5. Answer the following in reference to sequences

   a. Show the SQL code to create a sequence per the following:

   Sequence Name: testsequence

   Starts with: 100

   Increments by: 2

   b. Show the SQL command to display the next available sequence value (1st value).

   c. Show the SQL command to display the next available sequence value (2nd value).

   d. Show the SQL command to display the current sequence value.

   e. Show the SQL code to delete the sequence

Answer 1

Dear Student ,

As per the requirement submitted above , kindly find the below solution.

This demonstration is using Oracle Live SQL.

DUAL Table in Oracle :

• In oracle DUAL table which is having single row and single column.
• The name of the column is DUMMY.
• The DUMMY column is having value X.
• So from this value data type can be identified which is varchar2(1).
• Mostly this DUMMY column is used to select database objects like system date , user etc.
• Below screen shows the data from dual table in oracle
• getting system date
• 

************************************

USER function :

• USER function or user defined function in oracle is used execute block of code.
• In oracle user defined function can return value.

********************************

ROWNUM pseudocolumn :

• ROWNUM is a pseudocolumn in oracle.
• ROWNUM pseudocolumn is used to limit the number of rows from the table.

************************************

sequence in Oracle :

• sequence in oracle is used to create auto generated values for a column.
• In sequence starting value and increment value can be specified.
• Syntax :Create sequence nameoftheSequence start with value increment by value.

Question a :

create sequence testsequence
start with 100
increment by 2;

Question b :

select testsequence.nextval from dual;

Screen in Oracle Live SQL :

Question c:

select testsequence.nextval from dual;

Screen in Oracle Live SQL :

*****************************

Question d:

select testsequence.currval from dual;

*****************************

Question e:

drop sequence testsequence;

Screen in Oracle Live SQL :

*****************************

NOTE : PLEASE FEEL FREE TO PROVIDE FEEDBACK ABOUT THE SOLUTION.