Oracle Cursor

Oracle cursor


Cursor is a pointer in memory area called context area.

What is context are?

Context area is a memory area inside the Process Global Area (PGA) which helps Oracle server in processing an SQL statement by holding the important information about the statement.

This information include:
  1. Rows returned by a query.
  2. Number of rows processes by a query.
  3. A pointer to the parsed query in the shared pool.
Using cursor we can control the context area as it is a pointer to the same.

Types of cursors:

  1. Implicit cursors
  2. Explicit cursors

1. Implicit cursors:

  1. Automatically gets created by Oracle server when DML SQL statement gets executed.
  2. Users can not control the behavior of these cursors.
  3. Created in background for any PL/SQL block which executes an SQL statement. 

2. Explicit cursors:

  1. User defined cursors which means user has to create this cursor for any statement.
  2. Unlike implicit cursor user has full control over explicit cursor.

Create an explicit cursor:

This can be done in 4 steps-
  1. Declare
  2. Open
  3. Fetch
  4. Close
In case of implicit cursor Oracle performs all these steps automatically for us.

1. Declare cursor: 

Declaring a cursor means initializing a cursor into memory.

Syntax of declare,

CURSOR cursor_name IS select_statement;

2. Open cursor:

  • In order to put the cursor at work we have to open it first.
  • When we open the cursor the memory will be allotted to it., and it set put to the next step which is fetching the data from it.
Syntax of open,

OPEN cursor_name;

3. Fetch cursor:

The process of retrieving the data from the cursor is known as fetching the cursor.

Syntax of fetch,

FETCH cursor_name INTO PL/SQL variable;
Or
FETCH cursor_name INTO PL/SQL record;

4. Close cursor:

Closing statement of a cursor will releases all the resources associated with it.

Syntax of close,

CLOSE cursor_name;

Example of a Cursor:

DECLARE
CURSOR cursor_name IS select_statement;
BEGIN
OPEN cursor_name;
FETCH cursor_name INTO PL/SQL variable;
CLOSE cursor_name;
END;

More topics from DBMS to read:

References:

  1. Korth, Silbertz,Sudarshan, “Fundamental of Database System”, McGraw Hill
  2. Atul Kahate , “ Introduction to Database Management System”, Pearson Educations

Python Programming ↓ 👆
Java Programming ↓ 👆
JAVA EasyExamNotes.com covered following topics in these notes.
JAVA Programs
Principles of Programming Languages ↓ 👆
Principles of Programming Languages
EasyExamNotes.com covered following topics in these notes.

Practicals:
Previous years solved papers:
A list of Video lectures References:
  1. Sebesta,”Concept of programming Language”, Pearson Edu 
  2. Louden, “Programming Languages: Principles & Practices” , Cengage Learning 
  3. Tucker, “Programming Languages: Principles and paradigms “, Tata McGraw –Hill. 
  4. E Horowitz, "Programming Languages", 2nd Edition, Addison Wesley

    Computer Organization and Architecture ↓ 👆

    Computer Organization and Architecture 

    EasyExamNotes.com covered following topics in these notes.

    1. Structure of desktop computers
    2. Logic gates
    3. Register organization
    4. Bus structure
    5. Addressing modes
    6. Register transfer language
    7. Direct mapping numericals
    8. Register in Assembly Language Programming
    9. Arrays in Assembly Language Programming

    References:

    1. William stalling ,“Computer Architecture and Organization” PHI
    2. Morris Mano , “Computer System Organization ”PHI

    Computer Network ↓ 👆
    Computer Network

    EasyExamNotes.com covered following topics in these notes.
    1. Data Link Layer
    2. Framing
    3. Byte count framing method
    4. Flag bytes with byte stuffing framing method
    5. Flag bits with bit stuffing framing method
    6. Physical layer coding violations framing method
    7. Error control in data link layer
    8. Stop and Wait scheme
    9. Sliding Window Protocol
    10. One bit sliding window protocol
    11. A protocol Using Go-Back-N
    12. Selective repeat protocol
    13. Application layer
    References:
    1. Andrew S. Tanenbaum, David J. Wetherall, “Computer Networks” Pearson Education.
    2. Douglas E Comer, “Internetworking with TCP/IP Principles, Protocols, And Architecture",Pearson Education
    3. KavehPahlavan, Prashant Krishnamurthy, “Networking Fundamentals”, Wiley Publication.
    4. Ying-Dar Lin, Ren-Hung Hwang, Fred Baker, “Computer Networks: An Open Source Approach”, McGraw Hill.